Systems and methods for facilitating wireless network communication, satellite-based wireless network systems, and aircraft-based wireless network systems, and related methods

ABSTRACT

A wireless network system may include a source node having a first source wireless interface and a second source wireless interface, wherein the source node initiates a data transmission via the first source wireless interface. The wireless network system may also include a repeater node having a first and second repeater wireless interfaces, wherein the repeater node is configured to receive the data transmission on the first or second repeater wireless interface and to repeat the data transmission on the other of the first or second repeater wireless interface. The wireless network system also includes a destination node having first and second destination wireless interfaces, wherein the destination node is configured to receive the data transmission on the first or second destination wireless interface. A wireless network system may also include a satellite-based, wireless network system, including an earth station server, a satellite client, and a terrestrial client.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 12/364,769 filed Feb. 3, 2009, entitled “Systems and Methods for Facilitating Wireless Network Communication, Satellite-Based Wireless Network Systems, and Aircraft-Based Wireless Network Systems, and Related Methods.” The subject matter of this related application is incorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates generally to communication networks and more particularly to wireless network systems.

BACKGROUND

There are many kinds of networks that can be used to couple computers together for data communication. For example, a simple local area network (LAN), such as Novell® network or Appleshare® network can be used to couple together the personal computer in an office. Often, one or more network “servers” or “hosts” will influence data flow within the network and access to certain network functions such as a central file repository, printer functions, Internet gateways, etc. Other local area networks operate on a peer-to-peer basis without the use of servers.

A wide area network (WAN) is sometimes referred to as a “networks of networks.” The Internet is a WAN that has, of late, become extremely popular. The origins of the Internet date back several decades to a government-sponsored military/business/research WAN that was designed to remain operational even in the event of a catastrophic loss of a large portion of the network. To accomplish this goal, robust protocols and systems were developed, which allowed a geographically distributed collection of computer systems to be connected by means of a network that would remain operational even if a large portion of the network were destroyed.

While the use of Internet has been prevalent for many years now, its use has been limited by the arcane and often difficult commands required to access the various resources of the network. To address this problem, a protocol known as the “World Wide Web” or “WWW” was developed to provide an easier and more user-friendly interface to the Internet. With the World Wide Web, an entity having a domain name creates a “web page” or simply “page” which can provide information and, to ever greater extent, some interactivity with the web page.

The Internet is based upon a transmission protocol known as “Transmission Control Protocol/Internet Protocol” (or “TCP/IP” for short), which sends packets of data between a host machine, e.g. a server computer on the Internet, and a client machine, e.g. a user's personal computer connected to the Internet. The WWW is an Internet interface protocol which is supported by the same TCP/IP transmission protocol. Intranets are private networks based on the Internet standards, and have become quite common for managing information and communication within an organization. Intranets, since they subscribe to Internet standards, can use the same web browser and web server software as used on the Internet. Internets are, in many cases, supplementing or replacing traditional local area network protocols.

Most, if not all, of the data communication links between the various machines of most networks area hard-wired. That is, client machines are typically coupled to a server and to other client machines by wires (such as twisted-pair wires), coaxial cables, fiber optic cables and the like. In some instances, some of the communication links can be wireless communication links such as microwave links, radio frequency (r.f.) links, etc., but this tends to be rare with most LANs.

The majority of so-called wireless networks are radio modems for data communication, although there are some IR networks available that work over very short distances, such as within a single large room. However networks spanning larger areas will predominately use radio modems. GRE America, Inc of Belmont, Calif. sells a number of spread-spectrum modems that can be used for the transmission of digitally encoded information. A number of wireless network services such as Ricochet® network services (Ricochet is a subsidiary of Metrocom, Inc of Los Gatos, Calif.) combine a radio modem with a portable personal computer to allow the personal computer to connect to the Internet. The Ricochet system operates by providing a large number of r.f. data transceivers within a given geographic area, that is often attached to telephone poles, and that are coupled to centralized server that serves as a gateway to the Internet.

The assumption made by the Ricochet system designers is that a given radio modem coupled to portable computer will be in radio contact with one, and only one transceiver of the network. A data “packet” sent by portable computer via the radio modem will be received by the transceiver and broadcast through the Ricochet network until it reaches a Wide Area Processor or WAP, where it is transmitted by twisted pair over the internet to a Ricochet server connected to the Internet. Packets destined for a particular personal computer are received by the server of the Ricochet system, and are transmitted from each of the transceivers with the expectation that the radio modem of the destination portable computer will receive the data packets from one of those transceivers.

It should be noted that wireless communication systems such as Ricochet system exhibit a number of drawbacks. For one, if the radio modem of the personal computer is not within transmission range of one of the transceivers of the Ricochet network, a connection cannot be made to the network. Furthermore, the Ricochet network can create a great deal of “packet duplication” or “pollution” as copies of a particular data packet are multiply repeated, rather than routed. This packet duplication can also occur if a radio modem of a particular personal computer is radio transmission range of two or more transceivers can each receive the data packets, and each proliferates copies of the data packet across the Ricochet network. While duplicate packets are ultimately discarded, such duplicate packets increase data congestion in the network and increases the work that must be performed by the server. In addition, since data packets are transmitted from all the transceivers of the Ricochet network, there may be packet duplication at the personal computer if it is in contact with more than one transceiver of the Ricochet network, and the bandwidth available from each transceiver is reduced since each transceiver is transceiving each client-destined data packet on the network. Also, since the data is transmitted to the Internet over twisted pair, there is a 28.8K baud bottleneck in the system, resulting in average system performance of even less than 28.8K baud. It is therefore apparent that prior art wireless networks of the Ricochet network type lack robustness (i.e. the ability to maintain communication with the network under adverse conditions) and exhibit a number of inefficiencies such as data packet proliferation.

Cellular telephone system operates using a number of transceivers, where each transceiver occupies a “cell.” As a mobile telephone moves from one cell to another, an elaborate and expensive land-based system causes the mobile telephone to “handed-off” from the cell that it was previously in to the cell that is entering. As noted, the equipment and system used for the hand-off is expensive and, further, such hand-off sometimes fail, dropping the telephone connection. Furthermore, individual radios at a given cell can handle only one call at the time, which is inadequate for many computer network systems.

Amateur radio (“Ham”) operators have developed a peer-to-peer digital repeater system referred to as the AX.25 protocol. With this protocol, each peer repeats all data packets that it receives, resulting in rapid packet proliferation. In fact, with this protocol, so many packet collisions occur among the peers that the packets may never reach the intended peer.

Lastly there is abundant reporting in the literature, but it cannot be substantiated, that the U.S. military has a wireless communication system which allows digital information to be transmitted in a more robust and efficient manner. More specifically, it is suspected that the U.S. military has a system in which digital data can follow multiple paths to a server that may include one or more clients of the network. However, source code listings, or source code machine-readable form of these U.S. military systems remains secret and unavailable to the public. Some of the literature pertaining to this U.S. military technology is summarized below.

“Packet Radios Provide Link for Distributed Survivable Command Control Communications in Post-Attack Scenarios”, M. Frankel, Microwave Systems News 13:6 (June, 1983) pp. 80-108, discusses the SURAN (Survivable Radio Network) project and its relation to overall command and control communications (C³) development.

“Congestion Control Using Pacing in a Packet Radio Network”, N. Goweer and J. Jubin, Proceedings of Milcom 82, (New York: IEEE Press, 1985), pp. 23.1-23.6, describes a technique for pacing flow control used in the DARPA packet radio project.

“Current Packet Radio Network Protocols”, J. Jubin, Proceedings of Infocom 85 (New York: IEEE Press, 1985), pp. 86-92, is a systematic view of the various protocols currently used in the DARPA packet radio network. The article includes a discussion of packing, route calculation, maintenance of route and connectivity tables, acknowledgement schemes, and other mechanisms. The article also provides a discussion on how the various protocols interrelate and reinforce each other.

“The Organization of Computer Resources into a Packet Radio Network”, R. Kahn, IEEE Transactions on Communications COM-25.1 (January 1997), pp. 169-178, is a prospectus for the second generation of the DARPA radio project. This led to the development of the DARPA Bay Area Packet Radio experimental work in the mid to late 1970's.

“Advances in Packet Radio Technology”, R. Kahn, S. Gronemeyer, J. Burchfiel, R. Kunzelman, Proceedings of the IEEE 66z:11 (November 1978), pp. 1468-1496 is a survey of packet radio technology in the second generation of the DARPA packet radio project.

“Survivable Protocols for Large Scale Packet Radio Networks”, G. Lauer, J. Wescott, J. Jubin, J. Tornow, IEEE Global Telecommunications Conference, 1984, held in Atlanta, Ga., November 1984 (New York: IEEE Press, 1984) pp. 468-471, describes the SURAN network with an emphasis on network organizations and management protocols.

“Multiple Control Stations in Packet Radio Networks,” W. MacgGegor, J. Wescott, M. Beeler, Proceedings of Milcom 82 (New York: IEEE Press, 1982) pp. 10.3-5, is a transitional paper that describes design considerations involved in converting the DARPA packet radio network from single to multistation operation while eliminating the additional step to a fully hierarchical design. It focuses on the self-organizing techniques that are necessary in the multistation environment.

“Future Directions in Packet Radio Technology”, N. Shacham, J. Tumow, Proceedings of IEEE Infocom 85 (New York: IEEE Press, 1985), pp. 93-98, discuss new research areas in packet radio, with some references to SURAN developments.

“Issues in Distributed Routing for Mobile Packet Radio Networks”, J. Westcott, IEEE Global Telecommunications Conference, 1982 (New York: IEEE Press 1982, pp. 233-238, studies the issues involved in the DARPA packet radio network, prior to availability of signal strength sensing from the radio receivers as a hardware capability on which to build. The paper describes issues that must be considered in evaluating the usability of an RF link and gives details of the alternate route mechanism used in the DARPA system to smooth temporary RF propagation problems that appear in a mobile node environment.

“A Distributed Routing Design for a Broadcast Environment”, J. Westcott, J. Jubin, Proceedings of Milcom 82 (New York IEEE Press, 1982), pp. 10.4-1-10.4.5, is a detailed study of the problems involved in connectivity and routing table management in stationless packet radio, including a discussion of algorithms—proposed for the DARPA packet radio network.

There is, therefore, a great deal of literature describing packet radio systems. The prior art does not disclose, however, a packet-based wireless computer network that is both robust and efficient, wherein each client of the network can be efficiently and effectively in communication with a multiplicity of other clients and servers of the network, greatly multiplying the number of link choices available and, if conditions change, or if a better link to a server becomes known to a client, where the link for a client can be updated and improved.

The present disclosure describes a wireless network system which may be particularly well adapted for connections to a wide area network such as an Intranet or the Internet. The wireless network system may include one or more servers which are coupled to the wide area network, and two or more clients capable of communicating with the server or with each other via radio modems. The communication in the wireless network system may take the form of digital data packets, which are not too dissimilar from the TCP/IP data packets used over the Internet. However, the data packets of the present disclosure may also include data routing information concerning the path or “link” from the source of the packet to the destination of the packet within the wireless network. The data packets may include a code indicating the type of packet being sent.

In operation, for example, a client of the wireless network system of the present disclosure may have either a direct or an indirect path to a server of the wireless network system. When in direct communication with the server, the client is said to be “1 hop” from the server. If the client cannot reliably communicate directly with the server, the client will communicate with a “neighbor” client which has its own path (“link”) to the server. Therefore, a client may be able to communicate with the server along a link that includes one or more other clients. If a client communicates with the server through one other client, it is said to be “2 hops” from the server, if the client communicates to the server through a series of two other clients, it is said to be “3 hops” from the server, etc. The process of the present disclosure may include an optimization process which minimizes the number of hops from the clients to the servers, on the theory that the fewer the number of hops, the better the performance of the network. Optimization process may also factor in traffic and transmission reliability of various links to determine the optimal path to the server.

Some wireless network systems described herein may include at least one server having controller and a server radio modem, and a plurality of clients each including a client controller and a client radio modem. The server controller may implement a server process that includes the controlling the server radio modem for the receipt and transmission of data packets from clients of the network. The client controller may implement a client process including the transmission and receipt of data packets from the server and from other clients. The client process of each of the clients may initiate, select, and/or maintain a radio transmission path (“link”) to the server. As noted previously, this radio transmission path to the server may be either a direct path to the server (1 hop) or an indirect path to the server (multi-hop) through one or more clients. The client process of a particular client may also constantly search for improved paths to the server.

Some methods for providing wireless network communication described herein may include providing a server implementing a server process, and providing a server implementing a server process, and providing a plurality of clients, each client implementing a client process. The server process may include receiving data packets via server radio modem, sending data packets via the server radio modem, performing a “gateway” function to another network, and/or performing housekeeping functions. The client process may include the sending and receiving of data packets via a client radio modem, maintaining a send/receive data buffer in digital memory, and/or selecting links to the server. Again, the client process may choose a “best” link to the server that may be either a direct path or an indirect path through one or more other clients.

Some exemplary servers described herein may provide a gateway between two networks, where at least one of the networks is a wireless network. The gateway function of the server may make any desired translations in digital packets being sent from one network to the other network. The server may include a radio modem capable of communicating with a first, wireless network according to some examples of the present disclosure, a network interface capable of communicating with the second network (which may or may not be wireless and, in fact, may be a wired TCP/IP protocol network), and a digital controller coupled to the radio modem and to the network interface. The digital controller passes data packets received from the first network that are destined for the second network to the second network, and passes data packets received from the second network that are destined for the first network to the first network, after performing any necessary translations to the data packets. The digital controller may further maintain a map of the links of the first network and may provide a map to the first network clients on request. By maintaining a map of the first network links, the server may be able to properly address packets received from either the first network or the second network to the appropriate client of the first network, and may allow the client of the network to maintain and upgrade their data communication paths to the server.

Some network clients for a wireless communication network described herein may include a radio modem capable of communicating with at least one server and at least one additional client, and a digital controller coupled to the radio modem to control the sending and receiving of data packets. The digital controller may be further operative to determine an optimal path to at least one server of wireless network. The optimal path can be either a direct path to the server or an indirect path to the server through at least one additional client.

The methods and systems of the described herein may provide a wireless network that is both robust and efficient. Since each client of the network can potentially be in communication with a multiplicity of other clients and servers of the network, there may be a great number of link choices available. If conditions change, or if a better link becomes known to a client, the link may be updated and improved.

These and other possible attributes of the exemplary systems and methods described herein may become apparent upon reading the following detailed description and studying the various figures and drawings.

SUMMARY OF THE DISCLOSURE

In the following description, certain aspects and embodiments will become evident. It should be understood that the aspects and embodiments, in their broadest sense, could be practiced without having one or more features of these aspects and embodiments. It should be understood that these aspects and embodiments are merely exemplary.

One aspect of the disclosure relates to a wireless network system. The wireless network system may include a source node having a first source wireless interface and a second source wireless interface, wherein the source node is configured to initiate a data transmission via the first source wireless interface. The wireless network system may also include a repeater node having a first repeater wireless interface and a second repeater wireless interface, wherein the repeater node is configured to receive the data transmission on one of the first repeater wireless interface and the second repeater wireless interface, and to repeat the data transmission on the other of the first repeater wireless interface and the second repeater wireless interface. The wireless network system may further include a destination node having a first destination wireless interface and a second destination wireless interface, wherein the destination node is configured to receive the data transmission on one of the first destination wireless interface and the second destination wireless interface.

According to another aspect, a method for routing data packets in a wireless network system may include initiating at a source node a data packet transmission via a first source wireless interface, receiving at a repeater node the data packet transmission on one of a first repeater wireless interface and a second repeater wireless interface. The method may further include repeating the data packet transmission on the other of the first repeater wireless interface and the second repeater wireless interface, and receiving the data packet transmission on one of a first destination wireless interface and a second destination wireless interface of a destination node.

According to a further aspect, a satellite-based, wireless network system may include an earth-station server configured to transmit data packets to a secondary network. The wireless network system may also include a first satellite client of a plurality of satellite clients and a terrestrial client configured to maintain a table of known satellites, wherein the table is operable to store an address for each satellite client known to the terrestrial client. At least one processor may be associated with at least one of the earth-station server, the first satellite client, and the terrestrial client, wherein the

at least one processor is configured to establish a temporary route between the terrestrial client and the earth-station server via the first satellite client, ping a second satellite client, measure a response latency of the second satellite client, and determine, based on the measured response latency, whether the second satellite client has a reliable time-to-live. Further, if the second satellite client is determined to have the reliable time-to-live, the at least one processor may initiate a normal-mode handoff to the second satellite client. And, if the second satellite client is determined not to have the reliable time-to-live, the at least one processor may initiate a survival-mode handoff.

According to yet another aspect, a method for routing data packets in a satellite-based, wireless network may include maintaining at a terrestrial client a table of known satellites, wherein the table is operable to store an address for each known satellite client in the table. The method may also include establishing a temporary route between the terrestrial client and an earth-station server configured to transmit data packets to a secondary network through a first satellite client in a plurality of satellite clients. Further, the method may include pinging a second satellite client, measuring a response latency of the first satellite client, and determining, based on the measured response latency, whether the second satellite client has a predetermined reliable time-to-live. If the satellite client is determined to have the reliable time-to-live, the method may further include initiating a normal-mode handoff to the second satellite client. And, if the first satellite client is determined not to have the reliable time-to-live, the method may includes initiating a survival-mode handoff.

According to still a further aspect, a wireless network system may include a terrestrial client including a source wireless interface, wherein the terrestrial client is configured to initiate a data packet transmission via a source wireless interface. The wireless network system may also include a satellite client including an uplink interface and a downlink interface, the uplink interface operating at a first frequency and the downlink interface operating at a second frequency, the first and second frequencies being non-overlapping, wherein the satellite client is configured to receive the data packet transmission on the uplink interface and repeat the data packet transmission on the downlink interface. The wireless network system may further include an earth station server including a first destination wireless interface and a second destination wireless interface, wherein the earth station server is configured to receive the data packet transmission on one of the first destination wireless interface and the second destination wireless interface, repeat the data packet transmission on the other of the first destination wireless interface and the second destination wireless interface, and transmit the data packet transmission to a secondary network.

In yet another aspect, a method for routing data packets in a wireless network system may include initiating a data packet transmission via a source wireless interface associated with a terrestrial client. The method may further include receiving the data packet transmission on a first frequency at an uplink interface associated with a satellite client and repeating the data packet transmission on a second frequency at a downlink interface associated with the satellite client, wherein the first and second frequencies are non-overlapping. The method may also include receiving the data packet transmission on one of a first destination wireless interface and a second destination wireless interface associated with an earth-station server, repeating the data packet transmission on the other of the first destination wireless interface and the second destination wireless interface, and transmitting the data packet transmission to a secondary network.

In another aspect, a method for routing data packets in a wireless network system may include initiating a data packet transmission via a source wireless interface associated with a terrestrial client. The method may further include receiving the data packet transmission on a first frequency at an uplink interface associated with a satellite client and repeating the data packet transmission on a second frequency at a downlink interface associated with the satellite client, wherein the first and second frequencies are non-overlapping. The method may also include receiving the data packet transmission on one of a first destination wireless interface and a second destination wireless interface associated with an earth-station server, repeating the data packet transmission on the other of the first destination wireless interface and the second destination wireless interface, and transmitting the data packet transmission to a secondary network.

In a further aspect, a wireless network system may include an earth-station server configured to provide a gateway to a secondary network and a plurality of clients, each including a client controller implementing a client process, wherein the client process of at least one of the clients selects a transmission path to the earth-station server that is an indirect link to the earth-station server through at least one of the other clients, and wherein at least one of the clients is aircraft-based.

In an additional aspect, a method for routing data packets in a wireless network may include configuring an earth-station server to provide a gateway to a secondary network. The method may also include providing a plurality of clients, wherein each of the clients implements a client process operable to select a transmission path to the earth-station server that is an indirect link to the earth-station server through at least one of the other clients, and wherein at least one of the clients is aircraft-based.

Additional objects and advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosed embodiments.

Aside from the structural and procedural arrangements set forth above, the embodiments could include a number of other arrangements, such as those explained hereinafter. It is to be understood that both the foregoing description and the following description are exemplary only.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this description, illustrate several exemplary embodiments and together with the description, serve to explain the principles of the embodiments. In the drawings,

FIG. 1 is a pictorial representation of a wireless network system in accordance with the present invention;

FIG. 1 a illustrates a first tree structure of the data communication path or “links” of the wireless network system of FIG. 1;

FIG. 1 b illustrates a second tree structure illustrating optimized or “stabilized” data communication paths for the wireless network system of FIG. 1;

FIGS. 2 a-2 g, 2 h′-2 h″, and 2 i-2 o are used to describe a prototype of the wireless network system of FIG. 1, illustrating both the path connection and path optimization process;

FIG. 3 is a block diagram of a server, router, the first wireless network and the second network of FIG. 1;

FIG. 4 is a flow diagram of a server process operating on the server of FIG. 3;

FIG. 5 is a flow diagram of the “Process Packets Received From Client” step of FIG. 4;

FIG. 5 a illustrates a data packet processed by the process illustrated in FIG. 5;

FIG. 5 b is a flow diagram illustrating the process “Am I on Route?” of FIG. 5;

FIG. 5 c is a flow diagram illustrating the process “Data?” of FIG. 5;

FIG. 6 is a flow diagram illustrating the “Process Intermodal Information” process of FIG. 5;

FIG. 6 a is a flow diagram illustrating the process “Client Authentic?” of FIG. 6;

FIG. 6 b is a flow diagram illustrating the process “Put New Client In Tree” of FIG. 6;

FIG. 7 is a flow diagram illustrating the function “ADDSON(P,C)” of FIG. 6 b;

FIGS. 7 a and 7 b are used to illustrate the operation of the ADSON function of FIG. 7;

FIG. 8 is a flow diagram illustrating the “Delete Client From Tree” process of FIG. 6;

FIGS. 8 a-8 c illustrate the process of FIG. 8;

FIGS. 9 a-9 c illustrate the “Place Network Tree In Client Transmit Buffer” of FIG. 6;

FIG. 10 is a pictorial representation of the “Communicate with Network” process of FIG. 4;

FIG. 11 is a flow diagram of the process “Communicate With Network” of FIG. 4;

FIG. 12 is a block diagram of radio packet modem;

FIG. 13 illustrates a client, such as client A, B, C or D of FIG. 1;

FIG. 14 is a flow diagram of a client process running on the client of FIG. 13;

FIG. 15 is a flow diagram of the process “Radio Transmit and Receive Packet” of FIG. 14;

FIG. 16 is a flow diagram of the process “Perform Transmit/Receive Process” of FIG. 15;

FIG. 17 is a flow diagram of the process “Process Computer receive Packets” of FIG. 16;

FIG. 18 is a flow diagram of the process “Process Radio Received Packets” of FIG. 16;

FIGS. 18 a and 18 b are used to illustrate the process “Is It My Packet?” of FIG. 18;

FIG. 19 is used to illustrate the “Process Per Type Code” of FIG. 18;

FIG. 20 illustrates an initialization routine of the client process; and

FIGS. 21 a-21 d illustrate the process of FIG. 20;

FIG. 22 depicts an exemplary wireless network comprising transmission paths between a series of nodes in which each node implements an exemplary dual wireless interface;

FIG. 23 illustrates a block diagram of one possible configuration of a radio modem implementing an exemplary dual-wireless interface;

FIG. 24 depicts an exemplary LEO constellation;

FIG. 25 depicts an exemplary satellite-based wireless network;

FIG. 26 depicts a LEO satellite-based system operating in an exemplary normal mode;

FIG. 27 illustrates in flow chart form an exemplary overall satellite-based routing scheme;

FIG. 28 depicts an exemplary “Initiation Subprocess”;

FIG. 29 depicts an exemplary “LEO Beacon Subprocess”;

FIG. 30 depicts an exemplary “RTRT Subprocess”;

FIG. 31 depicts an exemplary “Route Discovery Subprocess”;

FIG. 32 depicts an exemplary “Reliable TTL Process”;

FIG. 33 depicts in detail an exemplary “Reliable TTL Handoff Process”;

FIG. 34 depicts an exemplary “Adjacent Plane Links Process”; and

FIG. 35 depicts an exemplary “Alternate Remote Route Process.”

FIG. 36 depicts an exemplary network in which an aircraft-based client may serve as a router for a terrestrial client.

FIG. 37 depicts an exemplary network in which aircraft-based clients and LEO clients may form a transmission link to an earth-station.

FIG. 38 depicts an exemplary network in which aircraft-based clients may extend a distressed LEO constellation operating in survival mode.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to exemplary embodiments. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

FIG. 1 illustrates an exemplary wireless network system 10. The wireless network system 10, which will also be referred to herein as a “first network”, is preferably in communication with a second network 12 via a digital communication bridge or router 14. The construction and operation of networks, such as second network 12, and bridges or routers, such as router 14, are well-known to those skilled in the art. It is preferred that the second network operates on the aforementioned TCP/IP protocols, i.e. the second network is the Internet or is a private Intranet. At times, herein, the second network will be referred to as simply the Internet, it being that other forms of a second network are also operable with the systems, apparatus, and process described herein. Again, the construction and operation of the Internet and Intranets are well-know to those skilled in the art. Likewise, routers, bridges, and other network devices such as hubs, gateways and Ethernet interfaces are well-known to those skilled in the art, and are available from a variety of sources including Cisco Systems, 3-Corn, Farillion, Asante, etc. In general, as a “network interface” may refer to any such device that allows a server of the wireless network system to communicate, directly and indirectly, with the second network.

The exemplary wireless network system 10 may include one or more servers 16, the single example of which is herein labeled S. It should be noted that the server 16, serves as a gateway in that it performs a translation service between the first network and the second network. For example, the data packets on the first network include links and data types that are only applicable to the first network. Therefore, such links and data types are removed from the data packets before they are transmitted to the second network which, as noted previously, preferably operates on a TCP/IP protocol. Conversely, data packets received from the second network are modified to include the links and data types before they are transmitted to the first network. Therefore, the data packets on the first or wireless network can be essentially “packages” or “envelopes” for TCP/IP data packets when they are destined for the Internet or received from the Internet. However, as will be discussed in greater detail subsequently, the data packets of the first network can be of types other than “data” types for TCP/IP formatted data. It should be noted that while only a single server S is shown in this example that, in most cases, multiple servers, each with their own gateway to the internet, will be used in the first network.

The exemplary wireless network system 10 further includes a number of clients 18, each including a client machine 20 and a radio modem 22. The client machine 20 can be any form of digital processor, including a personal computer (PC), a computer workstation, a personal digital assistant (PDA), etc. The client machine may be a personal computer (PC) made to the Microsoft Windows/Intel microprocessor (“Wintel”) standard, or the Apple Macintosh standard. Wintel and Macintosh compatible computers are commercially available from a variety of vendors. Likewise, computer workstations and PDAs are available from a number of vendors. Radio modems, such as the radio modem 22, are further available from a number of vendors. At least some embodiments disclosed herein may be implemented using radio modems produced by GRE America, Inc. which operate on a spread spectrum technology, and which provide good receiver sensitivity and repeater capabilities. These GRE America, Inc. radio modems are commercially available under the Gina trademark and operate in the 2.4 gigahertz or 900 megahertz bands with support for the packetized data transmission. The Gina band radio modems further include error detection and correction, can operate in asynchronous and synchronous modes, and can support data speed from 300 to 64 kbps. Furthermore, the Gina radio modems can operate in a point-to-point or point-to-multipoint mode.

A server process, to be discussed in greater detail subsequently, may be implemented on the server 16, and a client process, also to be discussed in detail subsequently, operates on each of the clients 18. The client process operates, at least in part, on the client machine 20. However, in alternative embodiment, the client process can operate on the controller of the radio modem 22 of the client 18.

In the exemplary wireless network system 10 illustrated in FIG. 1, the client 18A is in “direct” radio communication with the server 16 as indicated by the radio communication link 26. This will be referred to herein as “direct” or “1-hop” or “line-of-sight” connection with server 16. The client 18B, however, does not have a direct path or “link” to the server 16 due to an obstacle 24, such as a hill, large building, etc. Therefore, the client 18 communicates via a radio link 28 with client 22A which relays the data packets from client 18B to server 16. A client 18C has a direct line-of-sight to server 16, but is out of transmission range to the server 16. therefore, the client 18C transmits its data packets by a radio link 30 to client 18B, from where is relayed to client 18A via link 28, for eventual relay to the server S via radio link 26.

As noted in FIG. 1, 18D is in direct communication with server 16 via radio communication link 32. If client 18C detects the transmissions of client 18D, it will note that client 18D has less “hops” to server 16 than does client 18B, and will switch its link from client 18B to client 18D. This process is a part of the “stabilization” or “optimization” process of the network 10.

It will therefore be appreciated that the exemplary wireless network system 10 may be constantly attempting to optimize itself for the “best” data transmission. In the exemplary embodiments described herein, this optimization looks solely to the number of hops between the client and the server for the sake of simplicity. However, other factors can also affect the quality of the data transmission. For example, the traffic, of data packets through a particular client modem may be large, such that is better to route the data from neighboring clients through other clients, even though there may be more hops involved with the alternative routing. Also, some radio links may be less robust or may be slower than other links, such that optimization may result in a routing of data around the less robust or slower links, even though it may increase the number of hops to the server 16. Therefore, although the present embodiment looks at only one single factor in its optimization process, it will be appreciated by those skilled in the art that multiple factors can be used to stabilize or optimize the exemplary wireless network system 10.

It should also be noted that the exemplary wireless network system 10 may be quite robust in that it may survive the loss of one or more clients in the system. For example, if the client 18A is lost due, for example, to a power or system failure, the data packets of client 18C can be routed through the client 18D, and the data packets for the client 18B can be routed through clients 18C. Therefore, the wireless network system 10 may be highly robust and highly survivable under a number of adverse conditions.

In addition, some embodiments described herein may permit mobile communication within the wireless network system 10. For example, if the client 18D is a portable computer and is moved around within the wireless network system 10, it will opportunistically change its data communication path as better links become available. For example, if the client 18D is moved close to the client 18B, it may use the client 18B as its link to server 16. Also, any routing through the client 18D from other clients (such as 18C in this example) will be updated and optimized as the data path for the client 18D changes.

It should be noted that, in general, the network may operate the best and may be the most suitable if the radio modems and their client/controllers are never turned off. It may therefore be desirable to not have and on/off switch on the radio modem, so that the clients are always participating in the network traffic distribution. However, even if a radio modem is turned off, the remaining clients will re-route through other clients, as will be discussed subsequently

In FIGS. 1 a and 1 b, two “tree” structures are shown illustrating the various links that were discussed, by way of example, with reference to FIG. 1. The tree structure is maintained in the server S, and is transmitted to any client that may request it.

In FIG. 1 a, a tree indicates that client 18A is linked to a server 16 by a link 26, client 18B is linked by link 28 to a client 18A and by link 26 to a server, and client 18C is linked by line 30 to client 18B, by link 28 to client 18A and by line 26 to server 16. The client 18 D is in direct communication with the server 16 via radio link 32. Therefore, clients 18A and 18D are both “1 hop” away from the server 16, client 18B is “2 hops” away from server 16, and client 18C is “3 hops” away from server 16.

In the scenario where client 18C realizes it has a better connection to server 16 through the client 18D, the link 30 to client 18B is no longer used, and a new radio link 34 to client 18D is established. This is illustrated in FIG. 1 b. Now clients 18A and 18B remain 1 hop clients, client 18B remains a 2 hop client, but client 18C is upgraded from a 3 hop client to a 2 hop client. Therefore, the data transmission efficiency of the network has been “stabilized” or “optimized.”

It should be noted that the term “link” is used to convey both the connection to an adjacent client as well as the entire path from the client to a server. It will therefore be understood that when speaking of a link to an adjacent client, that this also implicitly includes all necessary links from that adjacent client to the server, i.e. a link is the entire path description from a given client to a given server.

FIGS. 2 a-2 o, an exemplary wireless point-to-multipoint network is prototyped to facilitate a discussion of the theory and operation of the disclosed embodiments present invention. In FIG. 2 a, a network 36 with 60 potential “nodes” 001 through 060 is illustrated. As used herein, a “node” can either be a client or a server. The nodes 014 and 016 have been arbitrarily selected as servers for the purpose of this example. The nodes 014 and 016 are marking servers with the large black dot replacing the leading “0” of those numerals. For the purpose of this example, it is assumed that a node can only communicate with an immediate adjacent node. Of course, in actual operation, nodes may be able to communicate with more distant nodes than its immediate neighbor nodes.

It should be noted, that in the notes incorporated of FIGS. 2 b through 2 k the leading “0”s have been deleted from client numbers, e.g., client 005 is referred as client 5 in FIG. 2 b. This notation is used for clients with respect to clients and servers and the notation should not be confused with any other uses of the reference numerals 1 through 60 in this document.

FIG. 2 b, a first client is designated at node 005 (hereafter “client 005”). For the purposes of this example, the Yen or “£” symbol is positioned next to the client 005. As noted previously, for the purpose of this example, we will assume that any particular node is only in radio communication range of a node that is adjacent in a horizontal, vertical or diagonal direction, i.e., in an immediately adjacent “neighbor”. In this instance, client 005 detects that there is a radio contact with node 014, which is a server (hereafter “server 014”). This server 014 and the client 005 will build a routing path or “link” between each other. This is accomplished by client 0005 transmitting a “I Am Alive” packet seeking a route to a server. The server 014, being within a radio transmission range, will respond and will add the client 005 to its routing table as its “left son.” The meanings of the “routing table” and the “left son” will be described subsequently. The routing table of the server 014 is therefore 014(005), and the route from the client 005 to the server 014 is 005>014. Again, this notation will be discussed in greater detail subsequently.

The network 36 than has a second client 6 added as indicated by the “£” symbol next to node 006 in FIG. 2 c. Second client 006 makes radio contact with client 005 and builds a routing path or a “link” to a server 014 through the client 005. Server 014 updates its routing table accordingly. This is accomplished by client 006 issuing an “I Am Alive” packet seeking a client repeater route to a server. Client 005 will respond and add client 006 to its routing table as its left son. The updated routing table of the server 014 is therefore 014(005)006)). The route from the user client node 006 to the server 014 is 006>005>014.

In FIG. 2 d, a third client 007 is added to the network 36 as indicated by the “£” symbol next to node 007. Client 007 establishes contact with client 006 and finds a path through clients 006 and 005 to server 014. This is accomplished by client 007 issuing a “I Am Alive” packet seeking a client repeater route to server 014. Client 006 will respond and add client 007 to its routing table as its left son. The updated routing table of the server 014 is then: 014(005(006(007))). The route from client 007 to the server 014 is: 007>006>005>014.

In FIG. 2 e, another client 016 has been added at node 016 as indicated by the “£” symbol. It should be noted that the client 016 can make radio contact with clients 005, 006, and 007. However, client 016 recognizes node 026 as being a server (hereafter “server 026”) and then connects directly to server 026. This is accomplished by client 016 transmitting a “I Am Alive” packet seeking a route to a server. The server 026 will respond and will add client 016 to its routing table and its left son. The updated routing table of server 026 is then 026(016). The routing from client 016 to the server 026 is 016>026.

In FIG. 2 f, a server routing table and a route for each client thus far in the example are illustrated. It should be noted that when client 016 came into existence, a shorter route was created for client 007 to a server, namely via client 016 to server 026. As noted in this figure, client 007 has made the adjustment to connect to server 026, thereby “stabilizing” or “optimizing” the network 26. Also, it should be noted that server 014 has deleted client 007 from its routing table, since client 007 is now using server 026 as its gateway to the Internet. This creates a universe of six nodes, of which two are servers and of which four are clients. The average “hop” distance from a client to a server is 1.5 hops. The remainder FIGS. 2 g-2 o further illustrate these concepts.

In FIG. 2 g, the network 36 illustrates an extreme example where 58 clients are connected to the two servers 014 and 026. FIGS. 2 h′ and 2 h″ show a fully “stabilized” or “optimized” network where the path or “link” from any client any client to a server is as short as possible, i.e. where there is few “hops” as possible. It should be noted that the optimization occurs dynamically during operation and without complex algorithms and look-up tables. As will be discussed in greater detail subsequently, the optimization occurs when clients “hear” transmission from other clients that have a better (i.e. shorter) path to a server.

FIG. 2 h′ shows the network as seen from the point of view of servers 014 and 026 and from the point of views of clients 001-client 031. In FIG. 2 h″, the network as seen from the point of view of clients 032-060, along with statistics for the overall network, are shown. In brief, in a universe of 60 nodes, of which two are servers and 58 are clients, the average hop distance from a client to a server is 2.36206897 hops.

In FIG. 2 i, the process of adding a new client 009 to the server is illustrated. The first time the client 009 came “alive” (i.e. became operational) it took five tries before node 009 found a client neighbor with a path to the server. The reason that it may take many tries to find a connection path is that multiple neighbors of client 009 are responding to the client 009 “I Am Alive” message via CSMA/CD (Carrier Sent Multiple Access/Collision Detection) protocol. The likelihood that any particular neighbor of client 009 will respond first is, essentially, random. Once client 009 hear from a neighbor that it does not have a path to a server, client 009 tells that neighbor not to respond to the next “I Am Alive” announcement from client 009. In consequence, client 009 keeps trying to find a path to the server until it succeeds. However, that path may not be the shortest path. In this example, the client 009 finds a path to the Internet server, resulting in updating of the routing table for the Internet server 014, as 014(005(006(007(008(009)))),004,003). The route or “link” from client 009 to the server is: 009>008>009>006>005>014.

In FIG. 2 j, a client 029 is finding a route to the server via one of its neighbors. It finds a route through 019, and is added to the routing table a client 019 as its left son. The routing table of server 014 is also updated, and the rout from user client 029 to the server is determined. However, this route is not an optimal route in that it includes a greater number of hops than necessary.

In FIG. 2 k, the “stabilization” or “optimization” process is illustrated. It was previously noted that the client 029 has a non-optimal path to a server. In order to improve this path client 029 will receive “help” from its neighbors starting with client 007. Client 007 currently has a route to server 014. Client 007 starts randomly probing its neighbors looking to a short route to a server. Client 007 finds a shorter route to client 026. Client 007 informs server 014 to drop client 007 from server 014's routing table, and client 007 informs server 026 to add client 007 to its routing table. Since client 029 was “downstream” from client 007, client 029 dramatically becomes switched to a route to server 026.

In FIG. 2 l, this process is repeated for client 008. Notably, client 008 shortens its route to server 026 by 1 hop. Client 009 cannot improve its route to server 026.

In FIG. 2 m, client 018 shortens its route to server 027 to 2 hops. This is despite the fact that the route to client 007 and 008 are a relatively efficient 3 hop links.

In FIG. 2 n, client 029 is optimizing its path. Client 029 eliminates 018 from its route by “leap frogging” past client 018 with the result of the shortest possible 3 hop route to server. Ultimately, therefore, client 029 route is improved from a 7 hop path to server 014 to the shortest possible 3 hop path to server 026. This result is dramatically accomplished with the efficiencies of clients 007, 008, and 018 also improving, and without the need for complex routing algorithms.

In FIG. 2 o, another example of individual dramatic routing is illustrated for client 044. This client node shortens its rout from 3 to 2 hops by switching server destinations. Client 044 drops out of the server 014's routing table and gets added to server 026's routing table.

The advantage of prototyping the system in FIGS. 2 a-2 o is that further optimizations become apparent. For example, if a great deal of network traffic is going to a particular node, it may be desirable to place a “passive repeater” at that node. A passive repeater is not a client, per se, but, rather, is a transceiver that receives and rebroadcasts packets. The passive repeater therefore effectively extends the range the range of the transmitting clients, and reduces data bottlenecks in the system. A passive repeater is also used for clients with long links to a server in that it can shorten the link by effectively allowing to skip some intermediate links. The prototyping of the system is also useful in that it shows that placing servers near the center of the network reduces the average link length (i.e. reduces the average number of client hops) in the network.

In FIG. 3, a block diagram of the server 16 of FIG. 1 is illustrated. In this instance, the server 16 includes a computer system 38 and a number of peripherals coupled to the computer system. The computer system 38 can be a personal computer system, a computer workstation or a custom data processor capable of implementing the exemplary processes disclosed herein.

By way of example, the computer system 38 includes a microprocessor 42 that is coupled to a memory bus 44 and to an input/output (I/O) bus 46. Typically also coupled to the memory bus 44 are random access memory (RAM) 48 and read only memory (ROM) 50. The RAM 48 is usually volatile (i.e. its contents are lost when power is removed) and is used for temporarily or “scratch pad” memory. The ROM 50 is non-volatile (i.e. its contents are not lost when power is removed), and typically includes the start-up instructions for the computer system 38. A number of peripherals are typically coupled to the I/O bus 46. For example a removable media drive 52 for a removable media 54 (such as a floppy disk, a Zip® disk, or a C/D ROM) is typically coupled to the I/O bus 46, as is a fixed or hard disk 56. Furthermore, a router 14 or bridge can be used to couple the I/O bus 46 to the Internet 12 as previously described. In addition, an RJ45 Ethernet interface 58 can be used to couple the computer system 38 to a local area network 60 and from there to the Internet 12 by a router 14, or the like, Also, a radio modem 62 (including a control section C, a radio section R, and an antenna 64 coupled to the radio section R) can be coupled to the I/O bus 46. The radio modem 62 can communicate with the network 10 including a number of nodes 66 by a wireless transmission of “radio link 68”. The assembly of the hardware of the server illustrate in FIG. 3 will be apparent to those skilled in the art.

In FIG. 4, an exemplary server process 70 of the present invention is implemented on the server 16. More particularly, the server process 70 can be implemented on computer system 38, within the control section of the radio modem 62, or partially in both of those places. In the embodiment shown, the majority of the server process 70 is implemented on the computer system 38. However it should be noted that the control section C of the radio modem 62 includes a microprocessor and memory and, with proper program instructions, can be made to implement the process 70 of FIG. 4, freeing the personal computer 38 for other tasks.

The server process 70 includes a server process control 72 and four subprocesses. More particularly, the subprocesses include a process 74 which processes received from clients, a process 76 which sends packets, a process 78 which communicates with the network, and a process 80 which performs housekeeping functions. Each of these processes will be discussed in greater detail subsequently.

In FIG. 5, the process “Process Packets Received From Clients” 74 of FIG. 4 is illustrated in greater detail. The process 74 begins at 82, and at step 84, the variable RETRY is set to 0. Next, a step 86 retrieves a packet from the client receive buffer, and a decision step 88 determines whether the path or “link” of the packet is same as the currently stored link in memory. If not, a step 90 updates the tree. If so, or after the updating of the tree in step 90, a decision step 92 determines whether it is “My Packet?” In other words, step 92 determines whether the packet being received by the server was intended for that server. If not, a decision step 94 determines whether that server is on route. If that server is on the route, but is not its packet, a decision step 96 determines whether the packet has already been repeated. If, not the packet is placed in the client transmit buffer. If decision step 94 determines that the server is not on the route, or the packet has already been repeated, or upon the completion of step 98, a decision step 100 looks for time-out. The time-out is provided by the server process control 72 such that the computer hardware resources on which process 70 are implemented can be shared among the four processes. More particularly, in most instances, the computer hardware resources are shared among the subprocesses 74-78 in a “round-robin” fashion well-known to those skilled in the art. However, it should be noted that at times the strict round-robin scheduling is not adhered to, as will be discussed subsequently.

If step 100 determines that a time-out has occurred, the decision step 102 determines whether the retry number RETRY is greater than the allowed, namely NUMRETRY. In its preferred embodiment, the number of retries RETRY are set at, perhaps, 2 or 3 so that the server does not tie up its resources with endless retries of process. If RETRY is greater than the NUMRETRY, the process is as indicated at 103. Otherwise, a step 104 increments RETRY by 1. In the absence of a time-out and in the absence of the number of retries being used up, process control returns to step 86.

If step 92 determines that the packet is for that server, a step 106 determines whether the packet is a data type. If not, a step 108 process “internodal information.” If so, a step 110 places the data in a server transmit buffer. After the completion of steps 108 or 110, process control is returned to step 100 to determine if there is a time-out.

In FIG. 5 a, an exemplary “data packet” 112 is illustrated. As it will be appreciated by those skilled in the art, a data packet is an associated string of digital information that is transferred and processed as a unit. The data packet 112 shown includes a header 114, a type 116 and data 118. The data 118 can be standard TCP/IP data. The header 114 includes the source address, the address of all hops along the way (i.e. the “link” of the data packet), and the destination address. Hops (i.e. clients and servers) that already have been traversed (i.e. have already forwarded the data packet) are indicated with an asterisk (“*”) symbol. The type 116 is, in this implementation, a two-digit code indicating the type of the data packet 112, as well as will be discussed in greater detail subsequently. The data section 118 of the data packet 112 includes the data associated with that packet. The data according to some embodiments is in the range of 128-1024 bytes in length.

In FIGS. 5 b and 5 c, respectively, the decision steps 94 and 106, respectively, are illustrated with respect to the data packet architecture of FIG. 5 a. The decision step 94 (“Am I On Route?”) of FIG. 5 is simply determined by process 120 “My Address In The Header?”. If yes, the process of FIG. 5 branches to step 96, and if no, the process of FIG. 5 branches to step 100. In FIG. 5 c, the decision step 106 “Data?” simplifies to a process 122 “Is the Type Equal to 14?”. This is because, in the present invention, a type 14 has been arbitrarily chosen to indicate a data type. If yes, the process of FIG. 5 branches to step 100, and if no, the process of FIG. 5 branches to step 108.

In FIG. 6, the step 108 “Process Internodal Information” of FIG. 5 is explained in greater detail. The process 108 begins at 124 and, in a multi-branch decision step 126, the type of the data packet is determined. If the type is a “01”, a step 128 places an acknowledgement and a “code seed” in the client transmit buffer, and the process is completed at 130. Acknowledgements and “code seeds” will be discussed subsequently. If the type is a “07”, a step 132 receives the client request for the network tree, and the process places the network tree in the client transmit buffer in a step 134. The process is then completed at 130. If, however, the type is “13”, a step 136 deletes the client from the tree and a step 138 determines whether a flag has been set. If not, the process is completed at 130. If, the flag has been set as determined by step 138, a step 140 puts a new client in the tree and the process is then completed at 130.

If decision step 126 determines that the “type is “05” a step 142 determines whether the client is authentic. The authentication process, which will be discussed subsequently, keeps unauthorized clients from being added to the network. If the client is not authentic, the process is completed at 130 and the client is not allowed to connect to the server. If a step 142 determines that the client is authentic, a step 144 determines whether the client is already in the server tree. If yes, the flag is set in a step 146 and process control is turned over to step 136 to delete the client from the tree. Since the flag has been set, step 138 branches the process control to step 140 and the new client is placed in the tree, after which the process is completed at 130.

The addition and removal of nodes from trees are well known in those skilled in the art. For example, in the book, incorporated herein by reference, SNOBOL 4: Techniques and Applications, by Ralph E. Griswald, Department of Computer Science, University of Arizona, Prentiss-Hall, Inc.,® 1975, ISBN 0-13-853010-6, algorithms for placing and removing clients from trees are discussed.

FIG. 6 a illustrates the process 142 of FIG. 6 in greater detail. More particularly, the process 142 begins at 148 and, in a step 150, a “seed” is chosen on the fly. Next, in step 152, a “one way” function is performed using the seed and a known authentication algorithm, and a one-way result is stored. Next, found in step 154, the seed is “camouflaged” and in a step 156, places an acknowledgement code and camouflaged seed in the client transmit buffer. The process is then completed at 158.

The purpose of the process 142 is to prevent unauthorized “clients” from accessing the network. For example, hackers may be prevented from accessing the network unless they can crack the authentication process, which is nearly impossible.

Authentication techniques are well known to those skilled in the art. For example, the book, incorporated herein by reference, Algorithms in SNOBOL 4, by James F. Gimpel, Bell Telephone Laboratories, John Wiley & Sons, a Wiley Interscience Publication,® 1976 by Bell Telephone Labs, Inc., ISBN 0-471-30213-9, describes authentication techniques using one-way seeds. See, in particular pp. 348-349 with back references. In brief, a “seed” is chosen “on the fly” such as by reading the system clock. The one-way function modifies the seed using an algorithm known to both the server and the clients. The one-way result, which in this instance is 4 bytes in length, is stored. The step 154 then “camouflages” the seed by dispersing the 4 bytes among perhaps 26 other bytes prior to transmitting the camouflaged seed. The receiving clients know which of the four bytes to use for their one-way function.

The process 140 “Place New Client In Tree” of FIG. 6 is illustrated in greater detail in FIG. 6 b. The process 140 begins at 160 and in a step 162, it is determined whether this is a “1 hop” client. If so, a decision step 164 determines whether it is a new client C. If so, the variable P is set to S in step 166 and the function “ADDSON” with the variables (P, C) is evoked in step 168. S, of course is the server or root of the tree. If step 164 determines that is not a new client C, or after the completion of the ADDSON function, the process ends at 170.

If step 162 determines that it is not a 1 hop client (i.e. C is a multi-hop client) a step 162 determines whether the parent P of client C is known to client C. If not, a step 174 determines the parent P from the header of client C. If the client C does know its parent, or after the completion of step 174, a step 176 receives parent P from client C. Next, in a step 178, the function ADDSON(P,C) is evoked, and the process is completed at 170.

In FIG. 7, the ADDSON(P,C) function is explained in greater detail. More particularly, function steps 168-178 begin at 180 and, in a step 182, the variables C, P are received. In this notation, the sting RSIB( ) refers to a string of right siblings, and the notation LSON( ) refers to a string of left sons. A step 184 sets RISB(C)=LSON(P). A step 186 sets a string FATHER(C)=P and a step 188 sets the string LSON (P)=N2 is an in-memory pointer that points to the memory location of nodes. The string FATHER provides a pointer from a child C to its father, which in this case is P. The process is then completed as indicated at 190.

In FIGS. 7 a and 7 b, the ADDSON function is graphically illustrated. In FIG. 7 a, a parent 192 has left a son 194 and a right sibling 196. The parent 192 and left son 194 have mutual pointers to each other, while the right sibling 196 has only a pointer to the parent 192. The left son 194 also has a pointer to the right sibling 196. When ADSON function is evoked with the argument (P, C) C is added as the left son 198 and the pointer in the parent 192 is updated to point to the left son 198. The left son 198 has pointers to the parent and to the new right sibling 194. The new right sibling 194 still has a point to the older right sibling 196, and both siblings 194 and 196 have pointers to the parent 192. It should be noted, under all circumstances, that the parent is only directly aware of the left son, in that it only has a pointer to the left son.

In FIG. 8, the process 136 “Delete Client From Tree” is illustrated in flow-diagram form. The process 136 begins at 200 and in a step 202, it is determined whether the target is equal to the left son. The “target” is, of course, the client to be deleted. If the target is the left son, a step 204 determines if there are other siblings. If not, the left son is deleted in a step 206. If there are other siblings, a step 208 makes the next sibling the left son, and then the left son is deleted by step 206. The process is then completed at 210. If step 202 determines that the left target is not equal to the left son, the target is found in a step 212, and is then deleted in a step 214. A step 216 then changes the sibling pointers, and the process is completed at 210.

FIGS. 8 a-8 c are several scenarios used to illustrate the process of FIG. 8. Assume that there is a tree structure as illustrated in FIG. 8 a. If a node “A” (i.e. a client A) of FIG. 8 a “s=disappears” all nodes (clients) 218 that used client A as a path to the server P are dropped from the network as illustrated in FIG. 8 b. With reference again to FIG. 8 a, if the node C disappears, the sibling B will simply reset its pointer to point to sibling D without any loss of service to any of the nodes. The lost nodes 218 of FIG. 8 b will need to re-establish themselves into the network as previously described.

FIG. 9 a is a tree structure that will be used to illustrate the step 134 “Place Network Tree In Client Transmit Buffer” of FIG. 6. Since the tree structure 220 is a logical construct, it must be represented in a form suitable for digital transmission. This form is illustrated in FIG. 9 b as a string 222. With reference to both FIGS. 9 a and 9 b, the string 222 represents the tree on a top-to-bottom, left-to-right basis. Therefore the string 222 indicates for the parent X that its left son is 3 with a right sibling B. For the parent 3, there is a left son 9 with a right sibling Z. For the parent Z, there is a left son 8, a right sibling 5, and another right sibling Q. For the parent Q, there is a left son R. Therefore, the tree structure 220 has been completely and compactly represented by the notation of the string 222.

The converting of the trees to strings and the reverse is well known to those skilled in the art. In short, a left parenthesis in the string indicates that a left son follows, and a comma in the string indicates that a right sibling follows. For example, the aforementioned book SNOBOL 4: Techniques and Applications describe the process for converting trees to “prefix form” as described above, and vice versa. The aforementioned book ALGORITHMS IN SNOBOL 4 likewise describes the process.

While the tree structure 9 a is useful for representing and traversing a tree data structure, it is not well-adapted for rapid searching for particular nodes. For this purpose, the table of FIG. 9 c is created to implement fast searching and other housekeeping functions. In this illustration, the table of FIG. 9 c includes four columns. The first column is the sequential element or “node” number, a second column 226 is the node name, the third column 228 includes the time stamp of the creation of the node, and the fourth column includes the actual physical memory location of the node. In this way, a particular node can be searched by element number, node name, time stamp, or memory location without resorting to the time consuming recursive search algorithms otherwise typically used to search tree structures.

FIG. 10 is a pictorial representation of a portion of the server of FIG. 3 that has been simplified to explain steps 78 of FIG. 4 “Communicate With Network.” The exemplary wireless network system 10 may include a number of clients and, perhaps, other servers, each of which has its own IP address. The radio modems of those clients and servers communicate with radio modem 62 of the server which provides digital data to the serial port of a server computer or host 38. A router, bridge or other device is used to connect the server to a network, such as TCP/IP network 12. Of course the radio packet modem 62 and the server computer 38 can be considered part of the exemplary wireless network system 10 as described previously. The combination of the server and the router or the like performs a “gateway” function, in that it provides translation services between the two networks 10 and 12.

Referring back to FIG. 4 the step 76 “Send Packets” simply involves sending the data packets stored in the client transmit buffer to the network 10 through the radio modem 62. Likewise, and in a straightforward matter, the step 78 “Communicate With Network” simply forwards the data stored in the network transmit buffer to the network through the router 14 or through another route, such as the Ethernet interface 58. The “Send Packets” and “Communicate With Network” processes will be easily understood by those skilled in the art. Again, the server process control 72 allocates system resources among the processes 74-80 on a round-robin basis.

In FIG. 11, the exemplary housekeeping process 80 of FIG. 4 is illustrated in greater detail. Since the housekeeping function 80 is of generally less importance than the other function of process 70, it is possible that housekeeping function will be interrupted with a branch to one of function s 74, 76 and 78 of FIG. 4.

More particularly, in FIG. 11, the housekeeping function 80 of FIG. 4 is illustrated in greater detail. The process 80 begins at 232 and, in a decision step 234, it is determined whether a flag is set. If not, at step 236, the next element is equal to 1, i.e. it is picking the first element on the list. If step 234 determines that a flag is set, the process 80 knows that the housekeeping has been interrupted in the middle of the list and therefore the next element is set equal to the stored mark point as indicated in step 238. Next, a step 240 determines whether if the end of the table has been reached. If so, the process is completed at 242. If the of the end table has not been reached, the element retrieved in a step 244, and then in a step 246, it is determined whether the current time minus the time stamp is greater than a predetermined interval. If it is, a step 248 deletes the client from the tree and from the table. This step 248 is performed to ensure that a client node that has dropped out the network 10 without informing the server is deleted from the server tree at some point in time. A suitable interval may be 15 minutes, or any interval set by a network manager. Process control then returns to step 240.

If step 246 determines that a node (i.e., a client) corresponding to the next element has cheeked-in within the time INTERVAL, a step 250 determines whether there is a heavy traffic on the server. If not, process control is returned to step 240. If there is a heavy traffic, a step 252 marks the place in the table corresponding to the current element (i.e., the marked point in the list is stored in memory) and then a step 254 determines the traffic type. Process control then branches to process 256 if it is heavy network traffic, 258 if it is heavy outgoing packet traffic, and process 2600 if it is heavy incoming packet traffic.

In FIG. 12, a radio modem 62 (which can be similar to all of the radio modems described herein) is illustrated in block diagram form. Again, the radio modem 62 is commercially available from GRE America, Inc. as the Gina spread spectrum radio modem, models 6000N-5 or 8000N-5. Spread spectrum technology gives good reliability and some transmission security in that a 127-bit cyclical code must be known by both the transmitting and receiving node. However, for true data security, encryption techniques, well known to those skilled in the art, should be used. Gina modems do include the option of 64-bit built-in encryption as an option.

It should be further noted that the Gina radio modem hardware can be modified to incorporate the server process (or the client process for the client radio modem) of the present invention by storing program steps implementing those processes into a ROM or programmable ROM (PROM) 262 of the radio modem 62.

The radio modem 62 includes a microprocessor 264 coupled to a bus 268. The microprocessor is an Intel 80C188 microprocessor in the present example. The PROM 262 (which currently stores 512 Kbytes of code) is coupled to the bus, as in RAM 268, a serial interface 270 and an HDLC converter 272. Coupled to the HDLC 272 interface is a transceiver interface 274, and coupled to the transceiver interface 274 is a CSMA/CD unit 276. A transceiver unit 278 with an antenna 280 is coupled to the CSMA/CD unit 276.

The devices 272 and 276 are used for error correction and noise cancellation, as will be appreciated by those skilled in the art. The CSMA/CD detects if two packets have “collided” producing indecipherable noise. If so, no acknowledgement of the packets is sent by radio modem 62 and the senders of the two packets will wait a short random period before resending their packets. Since the waiting period is random, there is little likelihood that the packets will collide a second time. The HDLC performs a checksum on the received packets and, if the checksum fails,

prevents the sending of the acknowledgement. This will cause the sending node to resend the packet after a random waiting period.

The currently used radio modems operate in the 902-908 MHZ frequency range at about 725 mW, and have an outdoor range of up to 12 miles, line-of-sight. These characteristics are a good compromise for a light to moderately dense network. If the network becomes very dense, it may be preferable to reduce the power, since this will reduce the number of clients that hear a given packet. Also, other frequency ranges are also suitable, such as the 2.404 to 2.478 GHz range.

The currently sold Gina spread spectrum radio models have their transmission (“baud”) rate artificially limited to 38.4 kHz. However, this artificial limit can be easily removed by a simple change to the program in PROM 262 to allow the modems to operate at 115.2 kHz, or nearly at full ISDN baud rates. At these baud rates, a single server can reasonably support three simultaneous WWW browser sessions and a dozen e-mail sessions. This compares very favorably to cellular networks which, as noted previously, can only support one user at the time. This also compares very favorably to the RICOCHET system which, since is limited to 28.8K baud, is not very useful for WWW browsing.

In FIG. 13, an exemplary client 18 including a computer 20 and a radio modem 22 of FIG. 1 is illustrated in greater detail. Again, the client computer 20 can be any suitable form of digital processor including personal compute, work station, PDA, etc. A computer 20 includes a microprocessor 282, RAM 284, and ROM 286. The microprocessor is coupled to the RAM 284 and the ROM 286 by a memory bus 288. The microprocessor 282 is also coupled to an input/output (I/O) bus 290 to which a number of peripherals 292 may be attached, including the radio modem 22. As before, the radio modem 22 includes a control C portion and a radio R portion, where the control portion of the radio modem 22 is coupled to the I/O bus 290. With brief reference to FIG. 12, the control portion C is everything but the transceiver unit 278 and the antenna 280, and the radio portion R corresponds to the transceiver unit 278. Also, as before, the client process running on the client 18 can run on the computer 20, in the control C portion of the modem 22, or partially on both processors. The client 18 typically includes other peripherals 292 such as a removable media drive 294 receptive to removable media 296, (such as a floppy disk or a CD ROM) and to a hard disk drive 298. Those skilled in the design of computer system will readily understand how the hardware of client 18 is assembled and used.

In some embodiments, uninterruptible power supplies and Global Positioning Systems (GPS) may be added to the client 18. The uninterruptible power supplies ensure that the clients stay on the network, and the GPS can be used in conjunction with directional antennas (such as phased array antennas) attached to the radio modem 22 to direct the transmission to the desired next node in the link. This increases the efficiency of the system, and reduces “packet pollution” of the network. The GPS unit can be coupled to I/O bus 290, or can be incorporated into the radio modem 22.

In FIG. 14, an exemplary client process 300 is implemented in the hardware of client 18. Again, this process can run on the microprocessor 282, or it can be partially or wholly run on the microprocessor of the controller C of the radio modem 22. In this exemplary embodiment, the process 300 runs on the computer portion 20 of the client 18. The client process 30 includes a client process control 302, a process 304 for radio transmitting and receiving data packet, and a process 306 for maintaining a first-in-first-out (FIFO) buffer for send and receive data packets in RAM 284 for the computer 20.

In FIG. 15, the exemplary process 304 of FIG. 14 is described in greater detail. The process 304 begins at 308 and, in a step 310; it is determined whether the client is on the network. If not, the client needs to get on the network before it can send data to the server. This connection process begins at 312 to determine whether it is out of tries in trying to reach the server. If not, it sends a 01 packet in a step 314 and waits to receive a 02 packet from the server or another client in a step 316. If it does not receive a 02 packet in response to 01 packet process control is returned to step 312 until it runs out of server tries. When it does run out of server tries, process control is turned over to step 318 which determines whether it is out of client tries. If yes, this particular client cannot reach either a server or another client and the process terminates at 320 with a failure. If it is not out of client tries in step 318, a 03 packet is sent in a step 321 and the client waits to receive a 04 from another client in a step 322. If a 04 is not received, the process control is returned to a step 318 until they are out of client tries.

If a 02 is received in a step 316 or a 04 is received in a step 322, then the client is in communication with the server or a client, respectively. In either instance, a step 324 stores the “link”, i.e., the path to a server, whether it is direct to the server or through one or more intermediate clients. Next, in a step 326, a 05 is sent to the link and a step 328 determines whether a 06 is returned. If not, the process is terminated as indicated at 320. If a 06 has been received, then a 07 is sent to the link in a step 330, and a step 332 determines whether a 08 is returned. If not, a step 334 determines if they are out of tries, and if not, process control is returned to step 330 to send another 07 to the link. If after a certain number of tries, e.g., 3 tries, a 08 is received in response to 07 transmitted by the client, the process terminates with a failure at step 320. If a 08 is received as determined by step 332, a random check-in time is set in a step 336. A random check-in time is set so that not all clients will try to check in with the server at the same time. Preferably, the random times will equally distribute the check-in times for the various clients equally within the aforementioned period INTERVAL. Finally, at this point, the client is connected into the network and the transmit/receive process is accomplished in a step 338. Of course, if the client was on the network as determined by step 310, the step 338 can be performed directly. The step 338 will be performed until there is a time-out of the transmit/receive process due to the round-robin scheduling by the client process control 302 (see FIG. 14).

In FIG. 16, the process 338 “Perfom/Transmit/Receive” is illustrated in greater detail. The process 338 has a transmit/receive process control 340 and the three subprocesses 342, 344 and 346. Again, the time allocated to the various subprocesses on a round-robin basis.

The subprocess 342 is the check-in routine where the client is required to check in on a periodic basis with the server to avoid being dropped from the server's routing list. As noted previously, the check-in start time is essentially random, and is within a given period INTERVAL. More particularly, the subprocess 342 begins with a decision 348 as to whether it is the proper time to check-in. If not, process control is immediately returned to process control 340. If it is check-in time, a 07 is sent to the server. If a 08 is received from the server, all is well and process control is returned to process control 340. If the expected 08 is not received, decision step 354 determines if there are any more tries. Typically, at least three tries will be allowed. If there are more tries, process control is returned to step 350. If there aren't any more tries, a step 356 will authenticate and send an 11 to the left son of the client that the client is removing itself from the network. Authentication prevents the situation where a “promiscuous” spooler could masquerade as a client and transmit an “11” packet with downstream client addresses, thereby disconnecting those downstream clients from the network. The client then marks itself as being disconnected or “off” of the network in a step 358, and a process control is returned to process control 340.

In FIG. 17, an exemplary process 344 “Computer Received Packets” is shown in flow diagram form. The process 344 begins at 360 and, in a step 362, the data is obtained from a buffer. Next, in a step 364, the header is added to the data including the link and the packet type “14” to indicate that this is a data-type data packet. Next, the data packet, complete with header, is transmitted in a step 366 and the process is completed at step 368.

FIG. 18 illustrates an exemplary process 346 “Process Radio Packets” of FIG. 16 in greater detail. The process 346 begins at 370 and, in a step 372, determines if the received packet is for it. If yes, a step 374 will process the packet per the code type, as will be discussed in greater detail subsequently. Then, a step 376 determines if the father node of the client has been marked. If not, a new, shorter link is created, since the packet was received without being relayed by the father node. If the father node has been marked, or after a new link has been created, the process terminates at 380.

If step 372 determines that it is not that client's packet, a step 382 determines if that client is on the route for the packet. If yes, a step 384 tests to see if the client is marked. If it is marked, it has already sent that packet and the process is completed at 380. If the client hasn't been marked, it marks itself in the header of the data packet and transmits the packet in a step 386. Process control is then given to step 376 to see if the client's link can be upgraded as discussed previously.

If step 382 determines that the packet is not for that client, and that the client is not part of the link, steps 388-392 still analyze the packet in process known as “pooning”. Since this client can hear this packet, there is an opportunity to upgrade its link. Step 388 determines whether the link to the last marked node plus one (i.e. the distance to the first unmarked node) is shorter than its own link. This is because this client is listening to the last marked node, and the number of hops through that last marked node is the number of hops of that last marked node plus one. If it is, the client's link is updated in a step 392 to this shorter link. If not, the alternative route is cached in case the client's current link becomes inoperative. Therefore, in the pooning process, the client listens to all packets to continuously and dynamically update its link to the best possible path.

In FIG. 18 a, an exemplary data packet 394 may include a header portion 396 including a link section 398 and a data type section 400, and a data portion 402. The link 398 indicates that the destination of this data packet is the node P. The two digit data type 400 indicates what type of data is being sent, and the data field 402 includes the actual data and is terminated within EOD (end of data) marker. This packet corresponds to the tree of FIG. 9 a. Since all upstream nodes (i.e. nodes Q, Z, 3, and X) are marked with asterisk (“*”), it is known that the data packet has passed through and has been marked by each of these nodes before reaching the node P. If, however, the data packet 394′ of FIG. 18 b is received where in only nodes X and 3 are marked, this means that the node 3 can hear the transmission of node (client) 3 directly. In this instance, there is no need to go through nodes Q and Z to reach server X. As a result, the new, upgraded link is from node P to node 3 to the server X. This is represented by the notation: X(3((P)).

The table of FIG. 19 is used to illustrate an exemplary process “Process Per type Code” step 384 of FIG. 18. The table of FIG. 19 includes tree columns 404, 406, and 408. The first column 404, lists the codes that can be received. These codes correspond to the 2 byte code 400 of the data packet 394 of FIG. 18 a. The second column 406 corresponds to the server responses to receiving such codes, and the third column 408 are the client responses to receiving the codes. We will now discuss each of the codes, in sequence.

When the server receives a 01 code its response is 02 code plus a one-way seed as discussed previously. Since 01 code is never intended for a client, it will ignore or “drop” the 01 coded data packets.

For the 02, 03 and 04 codes, the server will ignore or drop those data packets because these data packets are only intended for clients. If a client receives a 02, it responds with a 05 and a one-way response. In response to a 03, a client will send a 04 and a seed or a null. In response to a 04, the client will send a 05 and a one-way seed. Again, one-way seeds and responses to one-way seeds were discussed previously.

When a server receives a 05, if it has previously sent a 02 and if the 05 is authentic, then it will send a 06. Otherwise, it will drop the packet. When a client receives a 05, if it had previously sent a 04, and if the 05 is authentic, then it sends a 06. Otherwise, the client will drop the data packet. If the server receives a 06, it will drop the data packet. If a client receives a 06 after it sent a 05, then it will send a 07. Otherwise, it will drop the packet as well.

When a 07 is received from the server, it will immediately respond with a 08. Since 07 coded packets are never intended for clients, it will be dropped.

Data packets coded with an 08, 09, 10 or 11 are all dropped if received by a server. If a client receives a 08, it will update the tree or repeat the data. In response to a 09, a client will send a 10. In response to a 10, a client will update the tremor repeat the data. In response to a type 11, it sends an 11 to the left son with the address the departing node plus a 01 to reconnect to the network.

Data packets of type 12 and 86 are currently reserved. In response to a data packet type 13, a server will delete the sender. Since this is a server destination data packet only, if a client receives a data packet of type 13, it will drop the data packet.

Finally, if a server receives a data packet of type 14, it will send it to the network transmit buffer. If a client receives a data packet of type 14, it will send it to the computer transmit buffer.

FIG. 20 illustrates an initialization routine which connects the client CB to a server S through another client CA. The sequence is a s follows. As indicated by arrow a, client CB sends a 03 to client CA. In return, the client CA sends a 04 and a seed back to client CB as indicated by arrow b. Client CB then sends a 05 and a one-way response as indicated by arrow c to client CA, and client CA sends a 06 and an acknowledgement with a 05 to a client CD as indicated by arrow d. Then, client CB sends a 09 to client CA as indicated by arrow d. Then, client CB sends a 09 to a client CA as indicated by arrow e, and client CA sends a 10 and the link to the client CB as indicated by arrow f. Client CB then sends a 07 and the neighbor's addresses to the client CA as indicated by arrow g, and client CA relays the 07 and the neighbor's address to the server S as indicated by arrow g′. The server S, then sends a 08 and the tree to the client CA as indicated by arrow h, and the client CA relays the 08 and the tree to the client CB as indicated by arrow h′. At this point, the client CB has the link tree to the server S and the complete tree of the network in its memory.

FIGS. 21 a-21 d illustrate a portion of the server process which deals with determining a return path from a received data packet at a server. Assume, for example, the tree is known to the server is as illustrated in FIG. 21 a. this is the same tree as was illustrated in an example of FIGS. 9 a and 9 b. Then, assume that the server X receives the data packet from a client P as illustrated in FIG. 21 b. The simplest way of determining the reverse address is simply reverse the link section of the header portion of the data packet of FIG. 21 b to provide a return address of 21 c. However, if the part of the address of the header of the data packet of FIG. 21 b has been lost of corrupted during the transition process, the tree of FIG. 21 a can be used to reconstruct the return path. This is accomplished by jumping from parent to parent in reverse order as indicated to determine the return path. In this example, the reverse order parent jumping indicates that the original path to the server X was P>Q>Z>3>X, which, when reversed, gives us the proper reverse path, namely X(3(Z(Q(P)))). As will be appreciated by those skilled in the art, this type of reverse tree transversal is easily accomplished with a recursive function.

According to some exemplary embodiments, clients and servers may implement dual wireless interfaces to increase throughput between a source node and destination node. As described thus far, the client nodes and server nodes implement a single transceiver and interface, or a single-wireless interface. One inherent disadvantage of the single wireless interface may be a significant reduction in bandwidth per node in a transmission link. Specifically, transmitting data packets from a source node through one or more repeater nodes to a destination node may effectively reduce the bandwidth by one-half per node. As a consequence, for example, as applied to the widely used 802.11b interface, no more than three repeater nodes may be able to operate between a source node and a destination node without noticeable throughput loss to the destination node.

To minimize this possible limitation, servers and clients may, in some embodiments, implement dual wireless interfaces. Accordingly, at least some nodes may include a first source wireless interface and a second source wireless interface, one for receiving data packets and the other for simultaneously transmitting data packets. As indicated previously, a “node” as used herein refers to either to a client or a server. Where these nodes implement a hardware or software control that operates according to the conventions described below, this arrangement may allow a wireless network to achieve near 100% bandwidth through each repeater node. Accordingly, at least some examples of dual-wireless interfaces described herein may significantly reduce practical limits on the number of repeater nodes and, consequently, the number of hops between a source node and a destination node.

For example, FIG. 22 depicts an exemplary wireless network including transmission paths between a series of nodes in which at least some of the nodes (e.g., each node) implements a dual wireless interface. This exemplary system includes three clients 18 a, 18 b, and 18 c; a server 16; and two transmission paths 410 a and 410 b. Path 410 a carries data initiated at client 18 a and destined for server 16, while path 410 b carries data initiated at client 18 c and destined for server 16. Accordingly, with respect to the illustrated paths, 410 a and 410 b, clients 18 a and 18 b act as source nodes. And in each path, server 16 acts as a destination node. In addition, the first transmission path 410 a contains a repeater node, client 18 b, between the source and destination. Therefore, data packets traversing the path 410 a between source client 18 a and the destination server 16 have a two-hop route. And data packets traversing the path 410 b between client 18 c and the destination server 16 have a one-hop route.

To achieve near 100% throughput, for example, the network nodes may implement a controller configured to serve as a dispatcher in each node. To that end, the dispatcher may, in some embodiments, operate to route data packets according to the conventions described herein. One should note that any node in a wireless network system may, at times, act as a source, a repeater, and/or a destination node, depending on its function within a given transmission path. Thus, as used herein, a node acting as a source at a given time operates in “source mode,” a node acting as a repeater operates in “repeater mode,” and a node acting as a destination operates in “destination mode.” Further, because nodes may undergo frequent mode changes as data transmissions flow to and from network nodes, the control conventions described with reference to the example network of FIG. 22 should be viewed as applying to a particular “snapshot” in time.

In the case of a source node, for example, the controller may be configured, so that the dispatcher designates one of a node's wireless interfaces as the source from which it initiates all data transmissions. For example, in FIG. 22, source node 18 a has designated wireless interface 412 a as the source wireless interface. Accordingly, all data transmissions originating from the client 18 a, when acting in source mode, transmit from wireless interface 412 a of client 18 a. In this example, client 18 a initiates a data transmission from wireless interface 412 a to repeater client 18 b over the first hop along transmission path 410 a. Moreover, according to this convention, the dispatcher operates to ensure that all other data transmissions from client 18 a initiate from the same wireless interface 412 a, and the dispatcher correspondingly operates to ensure data transmissions do not initiate from the client's other wireless interface 412 b.

In the case of a repeater node, the controller may be configured so that the dispatcher allows the node to receive data packets on either of its two wireless interfaces and retransmit the data on the other of its two wireless interfaces. With reference again to FIG. 22, client 18 b acts as a repeater node, receiving incoming data packets from source client 18 a over the first hop of transmission path 410 a and retransmitting them to the destination node, server 16, on the second hop along transmission path 410 a. In this case, because repeater node, client 18 b, received data packets on its wireless interface 412 a, the dispatcher operates to retransmit the data packets on the other of client 18 b's wireless interfaces 412 b. It is important to note that the dispatcher routes the data in this manner, regardless of any designation the dispatcher has otherwise assigned to client 18 b's wireless interfaces 412 a and 412 b. In other words, as described above, the client 18 b's dispatcher may have assigned interface 412 b as the source wireless interface. That designation, however, applies only when the client 18 b acts in source mode. As a result, when wireless client 18 b operates in repeater mode, it repeats data transmissions on either of its wireless interfaces, which interface is determined as the wireless interface other than that on which the client received the transmission.

In the case of a destination node, the controller may be configured to allow a node to receive transmissions on either of a node's two wireless interfaces. Thus, the dispatcher may operate to allow a node acting in destination mode to receive data packets continuously on both of its wireless interfaces. For example, in FIG. 22, server 16 acts in destination mode, receiving two simultaneous and continuous data transmissions from two sources, client 18 b and client 18 c. On server 16's wireless interface 412 a, it receives a transmission initiated at client 18 c and transmitted along the one-hop path 410 b. Simultaneously, server 16 receives on its wireless interface 412 b a transmission from client 18 b along the second hop of path 410 a. In this manner, the destination node may maintain near 100% throughput.

FIG. 23 illustrates a block diagram of one possible configuration of a radio modem implementing a dual-wireless interface. This may be accomplished, in one respect, by modifying a radio modem at least similar to the radio modem 62 of the previously described client of FIG. 13 to resemble radio modem 62 a as shown in FIG. 23. The radio modem 62 a, illustrated in block diagram form, may incorporate a second transceiver unit 280 a, CSMA/CD 276 a, and transceiver interface 274 a. In this manner, the hardware may support the simultaneous receipt and transmission of data packets as described, by receiving incoming packets at a first transceiver unit 280 and retransmitting outgoing packets on a second transceiver unit 280 a. Further, the radio modem hardware may incorporate the controller by storing the logic of the above-described conventions into a ROM or programmable ROM (PROM) 262 of the radio modem.

In yet another aspect, the wireless network may comprise a satellite constellation in order to extend a wireless network and/or facilitate access to the Internet to remote users. As described herein, such an embodiment is referred to as a “satellite-based wireless network.” Such a system may be viewed as an extension into three dimensions of the terrestrial wireless network described above. In the described exemplary satellite-based system, data transmissions initiated on earth route through one or more satellites before making their way to a server located at earth (an “earth station server” or “ESS”) and passing into a secondary network, such as the Internet. Therefore, in the satellite-based system, satellites may operate in a client mode and may serve as repeater nodes of a transmission link. A satellite may be any communications device in the earth's atmosphere or orbit including, but not limited to, for example, a low-earth orbit satellite (LEO), mid-earth orbit satellites (MEO), a geosynchronous satellite (GEO), a zeppelin (e.g., a stationary zeppelin), a blimp, or a high-altitude balloon.

Extending the routing scheme described above for a terrestrial network, however, may require additional control due to the possible complications introduced by extending the network into three dimensions, e.g., by adding satellite clients to the network. These complications have made achieving, for example, TCP/IP capable routers on board satellites a significant hurdle for extending broadband wireless internet through the use of orbiting satellite routers and/or other conventional technologies. In one respect, using a constellation of LEO satellites to route data packets may advantageously avoid many latency-associated difficulties that arise in satellite implementations employing other types of satellites such as GEO satellites and MEO satellites, which require data packets to travel relatively greater distances. MEOs, for example, orbit between approximately 5,000 km and 10,000 km, and GEOs orbit at approximately 35,786 km above the earth's surface. While LEOs avoid many latency-related problems, however, they may introduce a host of other problems due to their orbital proximity to the earth's surface. Namely, LEOs' orbital proximity (within approximately 2,000 km of the earth's surface) causes them to travel with a greater degree of motion relative to clients located at the earth's surface (terrestrial clients). Therefore, wireless networks employing LEOs may need to account for additional mobility-related challenges to successfully implement a satellite-based broadband network using, for example, TCP/IP.

Accordingly, one practical challenge of achieving TCP/IP routing in a LEO constellation may be acquiring and maintaining a virtual circuit among, for example, a terrestrial client (“TC”), a LEO satellite, and earth station server (ESS). Significantly, the routing strategies implemented by the wireless network may greatly affect the overall performance of TCP communications carried across a satellite-based network. Accordingly, it may be desirable to provide a novel handoff scheme that enables TCP/IP routing on board a LEO satellite by providing a method that mitigates or overcomes at least some of the complexities of maintaining a virtual circuit from a TC and ESS through one or more LEO satellites.

The exemplary methods outlined below may accomplish this routing scheme via two operational modes, which are illustrated in FIG. 27: normal mode 446 and survival mode 448. Normal mode 446 may include a set of network processes that perform a data packet routing scheme when a requisite number of satellite-clients and earth station servers are operable, so that each of the TCs in the wireless network is able to build an optimal two-hop route to an ESS through an in-view LEO. Survival Mode 488, on the other hand, describes an optimal routing scheme adopted when, for example, a TC cannot find an optimal two-hop route to an ESS through an overhead LEO, but instead must revert to a constellation-wide mesh routing scheme to find an alternative optimal route through a plurality of LEO satellites. Several exemplary processes that may be implemented to achieve this desired operation are described in more detail below.

FIG. 24 and FIG. 25 depict an exemplary LEO constellation 413 that represents one possible arrangement for use in the described wireless network system. The illustrated constellation 413 may include, for example, seventy LEO satellites 416 traveling in polar orbit of the earth 414 at an escape velocity of approximately 17,000 miles per hour. The seventy satellites may be distributed among five orbital paths 418 collocated approximately five thousand miles apart at the equator. Accordingly, there are fourteen, approximately evenly distributed, satellites per orbital plane. Satellites travel along these planes in a longitudinal trajectory, moving from north to south over the horizon in one half orbit and from south to north in the other.

As illustrated in FIG. 25, the network may further include a number of ESSs 420 distributed on the earth's surface. As used herein, terms such as “earth,” “earth's surface,” “terrestrial,” “earth-based,” and similar terms, are used in a relative manner. For example, these terms are used to distinguish from altitudes associated with the satellites. Thus, these terms may not necessarily imply being attached to the ground or in a fixed position.

In the exemplary embodiment shown in FIG. 25, earth station servers may be collocated some five thousand miles apart. With this arrangement, the LEOs of this exemplary constellation have statistically three ESSs 420 in view at any given time. As used herein, a client or server is said to be “in view” when it is in communication range of another given client or server. Further, because each transition path consists of a single ESS 420, which serves as a destination node, second and third in-view ESSs 420 provide redundancy.

The following paragraphs explain in greater detail some exemplary systems and methods that may be used to support the above-described LEO handoffs while maintaining a substantially stable virtual circuit between the TC and ESS. These methods may comprise two operational modes: normal mode and survival mode. (See, e.g., FIG. 27.) In one aspect, a normal mode provides a novel handoff scheme that may be employed in an operational satellite-based wireless network. And, in another aspect, a survival mode provides countermeasures that may be desirable for maintaining a survivable network in the event that one or more clients or earth station servers is rendered inoperable, such as in the event of a global, catastrophic event. Together, these methods may address at least some of the complexities of extending a terrestrial network to a satellite-based wireless network.

FIG. 26 illustrates a LEO satellite-based system operating in an exemplary normal mode. According to this operational mode, the transmission path between the source node and destination node may contain a total of two hops and only one “satellite hop” through a satellite client. As shown in FIG. 26, an exemplary data communication initiates at a TC 422 acting in source mode. TC 422 may be a client located at earth and may be mobile or stationary. Data packets transmitted from TC 422 may ultimately seek a destination on a second network 424, such as the Internet. The second network may interface to the wireless network at a gateway of an ESS 420. For this reason, the ESS 420 may serve as the destination node in the transmission path from the TC 422. LEOs 416 travel overhead relative to the TC 422 in polar orbit. LEOs 416 a, 416 b, and 416 c orbit in a “local plane,” and LEOs 416 d and 416 e orbit in an “adjacent,” “remote” plane. Assuming an operational satellite constellation, such as the described exemplary LEO constellation, the TC 422 statistically will have three LEOs in view at any given time. For example, as shown in FIG. 26, local-plane LEOs 416 a and 416 b, and adjacent-plane LEO 416 d are located most proximately overhead the TC 422.

By the exemplary process described in detail below, the TC 422 will therefore build a route to the ESS 420 along a two-hop route comprising a first-hop 426 and a second-hop 428. For reasons described in more detail below, the TC will advantageously favor a route through a local-plane LEO over a remote-plane LEO due to the reliability and predictability of the local-plane LEO's time-to-live overhead. Accordingly, LEO 416 b receives data transmissions from the TC 422 on its uplink frequency over the first hop 426 in the transmission path and repeats it on its downlink frequency to the earth station server over the second link in transmission path 428. Because it may be assumed that the transmitted data packets contain TCP/IP structure, the earth station server need not perform any translation before passing the data packets on to a secondary network, for example, the Internet 424.

FIGS. 28-34 illustrate the described exemplary processes in chart form as a series of steps that take place in vertical, sequential order from top-to-bottom and execute at one or more TC, LEO, and ESS, as designated by vertical columns and according to the following description.

As used herein, a “mesh network” refers to a network that may allow for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached. In a terrestrial mesh network such as the exemplary ones described previously herein, for example, a route between a client and server and passing through one or more other clients will likely persist. In that case, alternative routes merely serve as an option to resolve the unlikely contingency that one or more nodes in the link between a source and destination becomes unavailable.

In contrast, LEO clients travel a great degree more with respect to the earth and, consequently, to terrestrial clients. As a result, each LEO remains overhead and in range of a terrestrial client for a limited time as it rises above the horizon and a short time later, falls below the opposite horizon, for example. This limited time a LEO spends in view above the horizon is hereafter referred to as a LEO's “time-to-live” (TTL). Because a satellite-based mesh contains routes through at least one LEO client, the TTL of each LEO repeater along the route introduces a necessary handoff. In this sense, a “handoff” refers to replacing a LEO client in an existing route with another LEO client in order to maintain a virtual circuit between the source and destination nodes. Due to the frequency of such handoffs, route maintenance in a satellite-based mesh may be a relatively more complex process than the process associated with a terrestrial network.

In one aspect, therefore, meshing in a satellite-based wireless system may result in implementing a route discovery and maintenance process that differs from a routing scheme associated with a terrestrial mesh network. For example, if route discovery in a satellite-based network were to begin as with a terrestrial network, as described in the exemplary embodiments above, the satellite-based route discovery process might be much less stable than the terrestrial route discovery process. Assuming, as before, an ESS maintains an in-memory tree of all of the clients that it is serving, once a TC has discovered a LEO through which to route, via an exchange of 03 and 06 packets, respectively, the TC and LEO would exchange 09 and 10 packets. Upon receiving the 10 packet, the TC (a) converts the payload data string of said 10 packet into its own in-memory tree, (b) finds its own address in said tree, and (c) counts the number of hops between it and the address of the server at the top of said tree. At this point in time, however, the route through the LEO would be unreliable due to the uncertainty of the new LEO's TTL. Moreover, randomly discovering other LEOs as potential alternate routes as in a terrestrial network may exacerbate the problem by forcing handoffs to other LEOs with unpredictable TTLs, thus making the network functional, but possibly unstable—requiring an unpredictable number of handoffs.

Accordingly, the Initiation Subprocess of FIG. 28, begins a slower, but more stable, route discovery process initiated by a LEO. This exemplary subprocess is one of four underlying sub-processes that may be performed at particular steps within the major exemplary processes described below. By this subprocess, a LEO constantly searches and identifies in-view ESSs.

Table 1 below provides a description of the exemplary data packet types referred to in the following description.

TABLE 1 Packet Description 00 A beacon packet for a roll call from neighbor clients 01 “I'm alive!” Ping to server 02 Server ACK from 01 followed by one-way challenge 03 “I'm Alive!” Ping to client(s) 04 Client ACK from 03 followed by one-way challenge 05 ACK followed by one-way response to Server or Client 04 06 One-way confirmation ACK from 05 from Server or Client 07 Ping to Server for route 08 ACK from 07 followed by route data 09 Ping to Client for route 10 ACK from 09 followed by route data 11 Signals 271 mode to clients 12 Signal to upstream clients to update routing table to add network of the client 13 Delete request from clients 14 Pseudo data packet 15 ACK from 14 16 End of Freeze

At a step 501, a LEO issues a 01 (I′m Alive!, ping) packet at short random intervals and receives in return a 02 (Server ACK from 01 followed by one-way challenge) from an in-view ESS. And, in a step 502, the ESS and LEO exchange 04 (Client ACK from 03 followed by one-way challenge) and 05 (ACK followed by one-way response to 04) packets for authentication.

According to the CSMA/CA protocol, multiple ESSs may receive the LEO-issued 01 packet, while only one ESS will respond with a 02 packet. In this respect, the ESSs may implement a variant of multi-homing by maintaining multiple potential routes, yet without transporting any payload data. These multiple routes would in that case respectively correspond to each LEO the ESS has sent a 02 packet. Therefore, after initiation, each one-hop route between a given LEO and ESS has exchanged no payload data (actual packet data that follows the packet header and identifies the source and destination of the packet) with a TC.

In another aspect, TCs in the wireless network may maintain a table of known LEOs including several fields of information relating to each LEO it identifies overhead. First among these fields, the array of known LEOs may store each known LEO's network IP address. According to some embodiments, these addresses correspond to static IP, IPv4, or IPv6 addresses assigned to each node (TC, LEO, and ESS). Other possible embodiments, however, may assign addresses using non-static protocols such as, e.g., network address translation (NAT) or dynamic host control protocol (DHCP). The TC may maintain these addresses in a table of known satellite clients located in transient or non-volatile memory using any of a variety of possible data structures well known in the art, including, for example, a stack, a queue, an array, or a hash table. In addition, the table of known LEOs may further comprise a time stamp field, which specifies the moment in time that the TC first identified and obtained the address of a LEO passing overhead, and a response latency time field, a measure indicative of a LEO's overhead proximity to the TC. The response latency of a satellite client may be, for example, a measured round trip response time (RTRT).

FIG. 29 illustrates an exemplary “LEO Beacon Subprocess,” another subprocess that may be implemented as part of the satellite-based route discovery process. By this subprocess, a TC discovers a LEO that has a one-hop route to an ESS and stores that LEO's address into its table of known LEOs. First, at a step 503, a LEO issues a 07 (ping to server for route) packet at short, random intervals. In response, an ESS with which the pinging LEO has a route responds with an 08 (ACK from 07 followed by route data). At a step 504, the LEO repeats the received 08 packet. And, finally, at a step 505, upon receiving the 08 packet, the TC reads the address contained in the 08 packet's payload data and enters the address in the TC's table of known LEOs along with a time stamp.

Accordingly, each execution of the LEO Beacon Subprocess creates an entry in a TC's table of known LEOs. When a TC's table of known LEO's is statistically full, the TC may then determine which, if any, address in the table represents a reliable temporary route through a LEO to an ESS. In this regard, a TC may treat its table of known LEOs as “statistically full” when, for example, it has identified a predetermined number of overhead, in-view LEDs. In the presently described exemplary embodiment operating in normal mode, a given TC expects three in-view LEOs during any given twenty-minute interval. Referring again to FIG. 26, for example, the TC 422 has three in-view LEOs 416 a and 416 b in its local plane, and 416 d, in its adjacent, remote plane. It should be noted, however, that the predetermined number of LEOs that renders the table of known LEOs as statistically full, serves primarily as a trigger for a TC to check whether any of its known LEOs has a reliable TTL. Accordingly, the TC may be configured, in the alternative, to treat its table of known LEOs as being statistically full at a lesser or greater number, as desired.

As described above, a TC will advantageously establish a two-hop route through a local-plane LEO for its property of having a predetermined, predictable reliable TTL. A TC may make this determination, in one aspect by performing the exemplary RTRT subprocess of FIG. 30. As illustrated in FIG. 30, at a step 506, the TC indexes its table of known LEOs and successively pings the address of each respective LEO, adding the round trip response time (RTRT) to the table of known LEOs for said LEO. In one aspect, the RTRT may be defined by the equation

${T_{RTRT} = \frac{2D}{c}},$ wherein T_(RTRT) represents round-trip-response time, D represents a distance between the first satellite and the terrestrial client, and c represents the speed of light. It is noted, however, that RTRT may represent only one appropriate measure. Other embodiments may employ other, equally appropriate measures that correspond to the transmission latency between a TC and LEO. Subsequently, at a step 507, the TC indexes its table of known LEOs and selects the address of the LEO with the shortest RTRT based on the assumption, for example, that the LEO is most proximate overhead among all LEOs known to the TC. In the event that multiple LEOs register the same RTRT value, the TC may simply select the address of the LEO most recently indexed.

Having selected the LEO most proximately overhead, the TC may next perform a Route Discovery subprocess to build a temporary route to the ESS with which the selected LEO has a one-hop route. For example, FIG. 31 illustrates an exemplary Route Discovery Subprocess in more detail. The subprocess begins at step 508, in which the TC and LEO build a route between each other by exchanging 03 (I'm Alive! ping to client) and 04 packets and 05 and 06 (One-way confirmation ACK from 05) packets, respectively, where, for the purpose of authentication, the 04 packet from the LEO contains a seed that prompts the TC to perform a one-way transformation, which it returns in the 05 packet. At step 509, the TC and LEO then exchange 09 (ping to client for route) and 10 (ACK from 09 followed by route data) packets, respectively. As previously described, this route data contains a string representation of the tree maintained in the router memory of the ESS associated with the LEO.

Upon receiving the 10 packet, the TC converts the payload data string of the route to the discovered ESS into its own in-memory tree; at step 510, finds its own address in the tree; and counts the number of hops between its address and the address of the ESS at the top of the tree. Having obtained a temporary route to the LEO, at step 512, the TC then updates the default gateway in its routing table with the address of the LEO. Immediately thereafter, the TC may issue a 12 packet with its address as the payload data to the address of the LEO. Upon receiving the 12 packet, the LEO may add the network of the address of the TC as a new network in its TCP/IP routing table. Finally, the TC and ESS then exchange payload data through the route at step 512.

It should be noted that in at least the satellite-based wireless and sub-orbital aircraft (see description below) embodiments, the TC, LEO, and/or ESS may employ an on-board operating system operable to manage packet routing by maintaining routing tables. In some embodiments, for example, a Linux operating system may be used by configuring the system to maintain and manage Linux routing tables. In such embodiments, therefore, maintaining routing tables may obviate the need to include routing information within a packet header, as was described with respect other embodiments herein (see e.g., header 114 in FIG. 5 a).

With a temporary route established, a TC may next attempt to discover a route through a LEO with a reliable TTL. When a newly-discovered LEO rises above the horizon, the TC does not know the LEO's longitude (whether said LEO is in a local orbital plane or a remote orbital plane). Referring back once again to FIG. 26, for example, LEOs 416 a, 416 b, and 416 d, each represent an in-view LEO, but only LEOs 416 a and 416 b, however, travel in TC 422's local plane. The “local plane” refers to the orbital path most closely aligned relative to the longitude associated with a given TC, while “remote plane” refers to all other orbital paths within the constellation. The significance of a LEO's traveling in a local plane follows from the fact that a LEO in a TC's local plane has a predetermined, reliable TTL. As a result, once a TC has established a route through a local-plane LEO, it may preemptively execute a handoff as the LEO's TTL approaches expiration.

FIG. 32 depicts an exemplary Reliable TTL Process, which describes the procedure for determining whether a given LEO has a reliable TTL. For example, beginning at step 513, a new LEO rises above the horizon and issues a 01 packet, thereafter receiving in return 02 packet from an in-view ESS. At a step 514, the LEO then determines whether it received a 02 packet from an ESS. If not, the LEO has no ESS in view and the system may execute an Adjacent Plane Links Process, for example, as shown at 454 of FIG. 27 and described in more detail below. Otherwise, the LEO has a reliable route through which it may seek to obtain the address of a LEO by performing the LEO Beacon Subprocess.

Still referring to FIG. 32, at step 515, the TC may issue a ping to the newly discovered LEO during the RTRT subprocess, thereby measuring the LEO's RTRT. If the measured RTRT falls within a defined RTTL time limit, then the TC knows the LEO is within the TC's local plane, and the system may perform an RTTL Handoff Process, for example, as shown at 452 of FIG. 27. Alternatively, if the RTRT exceeds the defined RTTL time limit, then the LEO is in a remote plane and the TC may restart the process, for example, beginning at step 513.

FIG. 33 depicts an exemplary Reliable TTL Handoff process, for example, as shown at 452 of FIG. 27. At this point, the TC has found a LEO transiting the horizon along a local orbital plane. Because the TC reliably knows the TTL of this LEO, it attempts to obtain a two-hop route through this LEO to an ESS and maintain the route until the predetermined reliable TTL approaches expiration, at which time the LEO will attempt to preemptively initiate a handoff to the next LEO rising above the horizon. Accordingly, at step 516, the TC may delete from its TC's table of known LEOs the address of the LEO discovered during the route discovery process at step 508. Next, at step 517, the TC may attempt to find the route to an ESS through the address of the LEO discovered at step 515 by, for example, executing the above-described exemplary Route Discovery Subprocess.

With the route through the TTL LEO established, the TC may then prepare for the next handoff, which the TC may preemptively initiate based on the approaching expiration of the predetermined reliable TTL. To prepare for the handoff, at step 518, the TC may delete from its table of known LEOs the address of the LEO discovered at step 517. Then, at step 519, exchange of payload data continues on the existing route and, at step 520, the TC performs the exemplary Reliable TTL Route Process 450.

When, at step 521, the TC determines the TTL of the existing route is approaching expiration, the TC executes, in step 522, a Route Discovery Subprocess to determine the address of the most recently discovered LEO. At step 523, the TC may then delete from its table of known LEOs the address of the LEO discovered most recently and, at a step 524, the exchange of payload data continues on the route discovered at step 520.

Still referring to FIG. 33 and with continuing reference to FIG. 27, at step 525, a new LEO rises above the horizon and performs a LEO beacon process. The TC then buffers the address of the newly transiting LEO and pings the address of the LEO and measures the RTRT at step 526. As before, if the measured RTRT falls within the RTTL time limit, the transiting LEO is within a local plane, and the TC may preemptively initiate a handoff when the TTL approaches expiration. If the RTRT exceeds the defined RTTL time limit, however, the LEO is not in a local plane and the system returns to step 525 and waits for the next LEO to rise above the horizon.

When operating in normal mode, a newly active TC joining the network acquires a route through a local-plane LEO. In this case, because the LEO has a one-hop route to an ESS, the route from TC to ESS contains a total of two hops. Furthermore, assuming all ESSs are operational, any given LEO has three ESSs in view: one to the north, to below it, and one to the south. A second and third ESS provide redundancy. In the unlikely event that all in-view ESSs of a LEO are inoperative, as may occur during a global, catastrophic event, for example, the LEO client may attempt repeatedly to route to a neighboring LEO in an adjacent plane until it acquires a route to an ESS. To accomplish this, the TC, the LEDs, and the ESSs may, according to some embodiments, perform the exemplary steps outline below. Meanwhile, the TC may continuously seek a two-hop route by performing step 510 of the exemplary route discovery subprocess.

FIG. 34 outlines exemplary steps of an exemplary Adjacent Plane Links Process, for example, as shown at 454 of FIG. 27. Beginning at step 527, the TC selects from its table of known LEOs the address of the LEO with the freshest time stamp then pings the address and measures the RTRT. If the measured RTRT falls within a defined “adjacent link time limit,” then the TC deletes the address from the table and repeats step 527. If, on the other hand, the TC finds the table of known LEOs maximally indexed and therefore empty, then it may be an indication that a network breakdown has occurred (e.g., some LEOs in the constellation are not functioning properly). In such case, the TC may exit the Adjacent Plane Links Process, and the system may switch to survival mode, for example, by performing an alternate remote route process, for example as shown at 456 of FIG. 27.

Otherwise, at step 528, the TC has found an acceptable route through an adjacent-plane LEO, and the network may remain in normal mode. In such case, the TC may execute a Route Discovery Subprocess and build a route to an ESS through the LEO of the selected address. Then, if during the Route Discovery Subprocess the TC determines that the number of hops to the ESS equals 2, the TC has discovered a local-plane ESS. In that event, the TC then stops looking for a route through an adjacent plane and instead branches to step 521 of the TTTL handoff process. If the TC does not determine that the number of hops equals 2, however, then at step 529, the TC determines whether there was a failure during the Route Discovery Subprocess. If so, it is possible that the network breakdown remains unresolved, and the system may enter survival mode by performing an Alternate Remote Route Process 456.

In still another, the wireless network system may be configured to implement a survival mode, which may implement the following exemplary logic to maintain a virtual circuit in the event that some LEOs and some ESSs become unavailable, such as in a global catastrophic event.

For example, when the network enters survival mode by reaching an Alternate Remote Route Process, for example, as shown at 456 of FIG. 27, it may operate according to a routing scheme at least somewhat similar to that as described above for a terrestrial network. In survival mode, the TC may not know the TTL of a given current route. As a result, a TC may not be able to predictably determine how long a route will persist and therefore may not be able to preemptively initiate LEO handoffs. Moreover, survival mode may be further defined by the fact that some LEOs and/or some ESSs are not operational. If, however, as few as a single, surviving ESS on earth remains operational, and a critical number of surviving LEOs remain operational, then the TC may obtain a multi-hop route through the surviving LEOs to the operational ESS by performing the exemplary Alternate Remote Route Process 456 of FIG. 27.

The exemplary Alternate Remote Route Process shown at 456 of FIG. 27, for example, illustrated in detail in FIG. 35, for example, beginning at step 530, the TC issues an 11 (signal survival mode) packet containing a survival TTL value as payload data. Next, at step 531, each LEO to receive the 11 packet repeats the packet recursively to neighboring LEOs until the TTL value expires. Upon expiration, all surviving LEOs in the constellation will have received the 11 packet. Accordingly, the survival TTL value should be set with a long enough duration to allow the packet to traverse the entire constellation. Then, at step 532, each surviving LEO issues a 01 packet. In response, at step 533, LEOs with line-of-sight to an ESS will receive from the ESS a 02 packet and then exchange with the ESS 05 and 06 packets for authentication. With this accomplished, these LEOs have established a one-hop path to an ESS.

Simultaneously, for example, each LEO that did not receive a responsive 02 packet (those without line of sight to an ESS) looks to find a route through a neighboring LEO. Accordingly, at step 534, each such LEO may issue a 03 packet repeatedly until it receives an 04 packet from a neighboring LEO. Upon receiving a responsive 04 packet from a neighboring LEO, at step 535, the LEO exchanges 05 and 06 packets with the neighboring LEO for authentication. If the neighboring LEO has an established multi-hop route to an ESS, then, at step 536, the LEO adds itself to the neighboring LEO's multi-hop route by exchanging 09 and 10 packets with the neighboring LEO at step 537. Otherwise, the LEO may loop back to step 534 and may retry, continuing to look for a route through a neighboring LEO.

At this point, the constellation of surviving LEOs and ESSs may approach a mesh. Meanwhile, at step 537, each LEO continually eavesdrops on the payload data of successive 08 packets from ESSs, which are repeated by LEOs above the ESSs. And, at step 538, if a LEO may find a shorter route to an ESS, the LEO may opportunistically adopt the shorter route from the payload data of the 08 packet to an ESS by updating its default gateway with the newly discovered LEO address. In this case, the LEO having just discovered a shorter route to an ESS may issue a 12 packet with its address as the payload data to the address of the newly discovered LEO. Upon receiving the 12 packet, the newly discovered LEO, which presents a shorter route to an ESS, may add the network of the address of the discovering LEO as a new network in its TCP/IP routing table.

Still referring to FIG. 35, in addition to all surviving LEOs receiving the 11 packet, which signals the network has entered survival mode, other TCs in the network receive the packet as well. Accordingly, all TCs in the network may perform the following steps to establish a first optimal route to an ESS. At step 539, the TC iteratively executes a Route Discovery Subprocess until discovering and building a multi-LEO-hop route to a surviving ESS. Once the TC finds a LEO with a route to an ESS, the TC at step 540, adds the address of the LEO to its table of known LEDs. Then, at step 541, the TC adds the address of said LEO to its TCP/IP routing table as its default gateway. Thereafter, the TC may issue a 12 packet with its address as its payload data to the address of the newly discovered LEO. Upon receiving the 12 packet at a step 542, the newly discovered LEO may then add the network of the address of said TC as a new network in its TCP/IP routing table. The TC then exchange payload data with the ESS.

At step 543, the TC eavesdrops on payload data of successively received 08 packets from ESSs (repeated by LEOs overhead) and attempts to discover a second optimal route—a shorter route through one of the LEOs to the address of an ESS. When the entire constellation of LEOs temporarily has optimized to the shortest routes to ESSs, the TC, at step 544, places other discovered routes of equal or greater number of hops (compared to the current route), along with an accompanying time stamp in a table of alternate routes. For example, the TC may in one aspect maintain the table of alternate routes as an ordered stack.

When a TC suddenly loses its route, for example, as a result of a LEO dropping below the horizon, the TC, at step 545, indexes its table and deletes routes with stale time stamps. The TC may also sort the array of alternate routes in ascending order, according to the number of hops. When implemented as an ordered stack, for example, the TC may “pop” the “next best” route from the top of the stack. As noted before, the best route, in some embodiments, may be defined with consideration of additional factors. As referred to herein, however, the best route may correspond to the path with the fewest hops. At step 545, the TC may then select the alternate route from the array and then return to step 540.

If, at any of steps 539 through 545, the TC receives a 08 packet with payload data indicating a two-hop route to an in-plane or adjacent-plane ESS, the TC at step 545 may perform the exemplary RTRT Subprocess. If the TC successively executes the RTRT subprocess, then, at step 547, it indexes its array of known LEOs and deletes any address of a LEO in the array with a stale time stamp and then, at step 548, branches to step 521 of the Reliable TTL Handoff Process 452 of FIG. 27 and waits. Alternatively, if the RTRT subprocess fails, then the TC returns to step 540.

Because a LEO may function as a repeater node in the network, it may in one aspect, advantageously implement the above-described dual wireless interface. The satellite 416 may receive uplink data transmissions from a terrestrial client on a repeater wireless interface, either of two satellite antennas. Preferably, the uplink and downlink frequencies may fall within the Ka-band, which is allocated internationally and capable of accommodating global broadband systems ranging from about 18 to about 40 GHz. For example, the satellite downlink frequencies may range from about 18.3 to about 18.8 GHz or from about 19.7 to about 20.2 GHz, while the uplink frequencies may transmit at about 30 GHz. By the exemplary methods described above, the client process may determine whether a packet is routed to an earth station server or to a neighboring satellite.

According to some embodiments processor on-board the LEO may run the Linux operating system, which maintains routing tables as described above. The software server program implemented on the earth station server and the client programs located on the LEO satellite and the terrestrial clients may be operable together via parallel processing to determine optimal routes by exchanging in-memory routing tree link information.

Transmissions to neighboring satellites may proceed over radio or laser intersatellite links (ISLs) 426. Further, each LEO may include of two RF interfaces, one on an uplink frequency and one on a downlink frequency—non-overlapping. The satellite required power output may range from, for example, about 50 to about 60 dbW, or from about 100 to about 1000 kW, for example, to overcome rain-induced attenuation associated with the high-frequencies transmissions in the Ka Band.

In still other embodiments, one or more mobile clients of a wireless network may be located on-board sub-orbital aircraft. For example, an aircraft may be equipped with a transceiver configured according to, for example, some embodiments of the present disclosure, and they may serve several desirable functions for facilitating broadband Internet access. For example, according to some embodiments, aircraft-based clients may serve as client routers for terrestrial clients, thereby permitting broadband Internet access to clients in locations where such service may not be otherwise available. In some embodiments, a wireless network path may include links between aircraft-based clients and LEO clients in order, for example, to reach an earth-station server. And, according to some embodiments, aircraft-based clients may serve as an extension of a LEO constellation by participating in a constellation-wide mesh, for example, when clients of a LEO constellation operate in survival mode.

According to a first exemplary embodiment, an aircraft-based transceiver may serve as a client router for a terrestrial client. This may be desirable because such example may make additional use of networking hardware in an aircraft equipped to provide passengers and/or crew with in-flight broadband Internet access (e.g., in-flight Wi-Fi access). In such embodiments, an aircraft may be outfitted with a transceiver and router to serve as a gateway to the Internet through an earth-station server. Possible transmission technologies for providing such wireless transmission between the aircraft and a server on the ground may include, for example, WiMAX (e.g., based on the IEEE 802.16 standard), 4G (also known as 3GPP Long Term Evolution), and CDMA (EV-DO RevA and EV-DO RevC).

To make additional use of the hardware in place for air-to-ground communications, a terrestrial client may route communications through an overhead aircraft configured as a client repeater to the Internet through an earth-station server. This may be accomplished by additionally configuring the aircraft's on-board transceivers to operate in client mode, for example, as described above with reference to FIGS. 14-21. Correspondingly, earth-station servers may be configured according to server processes, for example, as described above with reference to FIGS. 4-11. In this manner, a transceiver on board the aircraft may act as a client router on behalf of terrestrial clients, for example, in rural areas where high-speed Internet access may not be available through cable or DSL (Digital Subscriber Line).

FIG. 36 illustrates an exemplary embodiment in which an aircraft-based client may serve as a router for a terrestrial client. As shown, a terrestrial client 422 may acquire a two-hop path to an earth-station server 420 a through client network hardware located on board an aircraft 602. By, for example, the exemplary processes described herein, earth-station servers 420 a and 420 b may maintain in-memory tree link information about the known clients in the network. As the network topology changes due to, for example, an aircraft-based client moving out of range of a terrestrial client and/or an earth-station server, the route may adapt (e.g., automatically) in order to maintain a virtual circuit between both the terrestrial client and earth-station server.

As shown in FIG. 36, for example, as aircraft-based client 602 loses line of sight of earth station server 420 a, it may come into range of earth-station server 420 b and replace its air-to-ground transmission link with a link to server 420 b. Similarly, by the same client and server processes, for example, client 422 may establish a two-hop transmission path through another aircraft-based client (not shown) as it passes within line of sight of overhead.

According to some embodiments, for example, the exemplary embodiment shown in FIG. 37, aircraft-based clients and LEO clients may together form a transmission link to an earth-station. For example, LEO clients, aircraft-based clients, and/or terrestrial clients may each be configured to operate in client mode according to, for example, the exemplary client processes described herein with reference to FIGS. 14-21. Accordingly, an aircraft-based client and a LEO client each may serve as nodes through which data transmissions may pass to reach an earth-station server. Moreover, data transmissions may be initiated from either terrestrial clients or from subscribers on-board an aircraft.

As shown in this example, a terrestrial client 422 may exchange data packets with an earth-station server 420 along the three-hop route comprising, for example, links 604 (terrestrial client 422 to aircraft-based client at 602), 606 (aircraft-based client at 602 to LEO), and 608 (LEO to earth station server 420). Such an exemplary transmission link may arise, for example, when an aircraft-based client does not have line of sight to an earth-station server, but is able to route indirectly through a LEO. Similarly, a subscriber on board an aircraft may exchange data packets with an earth station server along the two-hop route comprising, for example, links 606 (aircraft-based client at 602 to LEO) and 608 (LEO to earth station server 420).

According to some embodiments, aircraft-based clients may extend a distressed LEO constellation operating in survival mode. For example, an aircraft-based client router may be configured to operate as a client in survival mode, as described in FIGS. 27 and 35. By serving as one or more links along a transmission path between a terrestrial client and an earth station server, aircraft-based clients may participate in a constellation-wide mesh, for example, when one of the LEOs or earth station servers becomes inoperable, such that a reliable two-hop link through one LEO is not available or is unreliable.

Referring to FIG. 38, for example, a two-hop link from terrestrial client 422 to earth station server 420 a is unavailable or unreliable. As described above with regard to survival mode in a LEO constellation, for example, clients receiving packets signaling survival mode may cause a large portion of the network (e.g., the entire network) to approach a mesh. In this exemplary case, aircraft-based client 602, configured to operate in the same manner as a LEO client, may participate in the constellation-wide mesh by acting as a node between a second and third hop, 612 and 614 respectively, thereby forming a complete transmission path between the terrestrial client 422 and earth station server 420 b.

It should be noted that providing broadband Internet access to aircraft passengers and/or crew is not a necessary component of the aircraft-based routing embodiments. Rather, it is mentioned merely for the possibility of simultaneously providing broadband access to subscribers on-board an aircraft and to terrestrial clients using pre-existing aircraft-based networking transmission and routing hardware.

Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the exemplary embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. In particular, the exemplary satellite-based wireless network routing system described herein may apply to several possible configurations or constellations and does not imply any requisite number or arrangement of satellites. Furthermore, though this disclosure seeks to provide, among other things, improved methods and systems for routing TCP/IP data packets, it may equally apply to other transmission protocols. 

What is claimed is:
 1. A satellite-based, wireless network system comprising: an earth-station server configured to transmit data packets to a secondary network; a first satellite client of a plurality of satellite clients; a terrestrial client configured to maintain a table of known satellites, wherein the table is operable to store an address for each satellite client known to the terrestrial client; at least one processor associated with at least one of the earth-station server, the first satellite client, and the terrestrial client, wherein the at least one processor is configured to: establish a temporary route between the terrestrial client and the earth-station server via the first satellite client; ping a second satellite client; measure a response latency of the second satellite client; determine, based on the measured response latency, whether the second satellite client has a reliable time-to-live, wherein, if the second satellite client is determined to have the reliable time-to-live, initiate a normal-mode handoff to the second satellite client; and wherein, if the second satellite client is determined not to have the reliable time-to-live, initiate a survival-mode handoff.
 2. The system of claim 1, wherein the plurality of satellite clients comprises a constellation of low-earth orbit satellites.
 3. The system of claim 1, wherein the secondary network comprises a computer network.
 4. The system of claim 1, wherein the data packets conform to TCP/IP protocol.
 5. The system of claim 1, wherein the at least one processor is configured to update a routing table on the terrestrial client, such that a default gateway associated with the terrestrial client contains an address of the second satellite client between the terrestrial client and the earth station server.
 6. The system of claim 1, wherein the table of known satellites is configured to store a time-stamp field and a response latency field.
 7. The system of claim 1, wherein the response latency is a round-trip-response time defined by the equation T_(RTRT)=2D/c, wherein T_(RTRT) represents round-trip-response time, D represents a distance between the first satellite and the terrestrial client, and c represents the speed of light.
 8. The system of claim 1, wherein the at least one processor is configured to determine a first alternative route via the plurality of satellite clients by exchanging in-memory routing tree link information.
 9. The system of claim 8, wherein the at least one processor is configured to maintain a table of alternate routes comprising at least one newly discovered route.
 10. The system of claim 8, wherein the at least one processor is configured to analyze at least one of the data packets to determine if the at least one data packet has been sent on a second alternative route unknown to the terrestrial client.
 11. The system of claim 10, wherein the analyzing comprises counting a number of hops between a source node associated with the at least one data packet and the terrestrial client.
 12. The system of claim 11, wherein the at least one processor is configured to sort the table of alternate routes and replace the first alternative route with the second alternative route when the terrestrial client loses the first alternative route.
 13. A method for routing data packets in a satellite-based, wireless network, the method comprising: maintaining at a terrestrial client a table of known satellites, wherein the table is operable to store an address for each known satellite client in the table; establishing a temporary route between the terrestrial client and an earth-station server configured to transmit data packets to a secondary network through a first satellite client in a plurality of satellite clients; pinging a second satellite client; measuring a response latency of the first satellite client; determining, based on the measured response latency, whether the second satellite client has a predetermined reliable time-to-live; wherein, if the satellite client is determined to have the reliable time-to-live, initiating a normal handoff to the second satellite client; and wherein, if the first satellite client is determined not to have the reliable time-to-live, initiating a survival-mode handoff.
 14. The method of claim 13, wherein the plurality of satellite clients comprises a constellation of low-earth orbit satellites.
 15. The method of claim 13, wherein the secondary network comprises a computer network.
 16. The method of claim 13, wherein the data packets conform to TCP/IP protocol.
 17. The method of claim 13, further comprising updating a routing table on the terrestrial client, such that a default gateway associated with the terrestrial client contains the address of the second satellite client between the terrestrial client and the earth station server.
 18. The method of claim 13, wherein the table of known satellites is configured to store a time-stamp field and a response latency field.
 19. The method of claim 13, wherein the response latency is a round-trip-response time defined by the equation T_(RTRT)=2D/c, wherein T_(RTRT) represents round-trip-response time, D represents a distance between the first satellite and the terrestrial client, and c represents the speed of light.
 20. The method of claim 13, further comprising determining a first alternative route via the plurality of satellite clients by exchanging in-memory routing tree link information.
 21. The method of claim 20, further comprising maintaining a table of alternate routes comprising at least one newly discovered route.
 22. The method of claim 20, further comprising analyzing at least one of the data packets to determine if the at least one data packet has been sent on a second alternative route unknown to the terrestrial client.
 23. The method of claim 22, wherein the analyzing comprises counting a number of hops between a source node associated with the at least one data packet and the terrestrial client.
 24. The method of claim 20, further comprising sorting the table of alternate routes and replacing the first alternative route with the second alternative route when the terrestrial client loses the first alternative route. 